This Study is a FIH Study Which is Required to Understand the PK Characteristics, MTD, RP2D and Safety Profile.

Inclusion Criteria: * 1\. A male or female aged ≥ 18 and \<75 years old. * 2\. The following three points are evaluated by the investigator and are deemed suitable to participate in the study: a) The subject fully understands the requirements of this study and voluntarily signs a written informed consent form; b) Be able to comply with the medication requirements of this study as well as all study related procedures and assessments; c) Not deemed as potentially unreliable and/or uncooperative. * 3\. An ECOG physical status score is ≤ 2 and an expected survival is ≥ 3 months. * 4\. Relapsed or refractory acute myeloid leukemia (AML) that meets the following criteria will be included in Phase Ⅰa : Patients diagnosed with AML according to the 5th edition of the World Health Organization (WHO) Classification of Haematolymphoid Tumours: -Myeloid and Histiocytic/Dendritic Neoplasms (Khoury et al., 2022), including any subtype except for acute promyelocytic leukemia (APL). These patients must have received at least one previous treatment and have failed to current standard treatments that provide clinical benefit. Note: The following diagnostic criteria must be met for relapsed/refractory AML: (1) Relapsed AML: Leukemia cells reappear in the peripheral blood or bone marrow blast cells exceed 5% after complete remission (CR) (excluding reasons such as bone marrow regeneration post-consolidation chemotherapy) or there is extramedullary infiltration by leukemia cells. (2) Refractory AML: Initial cases that are unresponsive after two cycles of standard regimen treatment; recurrence within 12 months after CR and consolidation therapy; recurrence beyond 12 months with ineffectiveness of conventional chemotherapy; those who have relapsed twice or more; or persistent extramedullary leukemia.; -5. Phase Ib tentatively includes patients with hematologic malignancies that meet the following criteria: relapsed or refractory AML subjects who have received at least one previous treatment and have failed to current standard treatments that provide clinical benefit, and MDS subjects who are diagnosed according to the 5th edition of the WHO Classification of Haematolymphoid Tumours-Myeloid and Histiocytic/Dendritic Neoplasms (Khoury et al., 2022) and are classified as high-risk or very-high-risk according to the Revised International Prognostic Scoring System (IPSS-R) (Greenberg et al., 2012). The specific tumor type will be determined based on the results of the Phase Ia trial and may be extended to other hematologic malignancies. Note: Subjects with myelodysplastic syndromes with excess blasts (MDS-EBs) type 1 (MDS-EB1) or type 2 (MDS-EB2) may be considered for inclusion. The EB type has a higher risk of transformation to AML than other subtypes and may have greater clinical benefits. * 6\. The test of CD33 and/or CD123 for Phase Ia and Ib subjects in this study will be required to be positive, and patients with any level of CD33 and/or CD123 positivity were allowed to be included. Note: The positivity and expression levels of CD33 and CD123 were determined by each site. * 7\. Consent to bone marrow biopsy and aspiration, and consent to implantation of medical devices such as peripherally inserted central catheter (PICC), or venous access port, or central venous catheter (CVC) (if applicable) for long-term intravenous drug administration. * 8\. Patients have recovered from toxicity of prior first-line therapy, i.e., Grade 1 toxicity according to the National Cancer Institute Common Terminology Criteria for Adverse Events (NCI CTCAE) V5.0, with the exception of toxicities such as alopecia, fatigue, and other toxicities deemed by the investigator to be of no safety risk to the patient, as well as hematological toxicities related to the tumor. * 9\. Substantial normal function of major organs with screening laboratory tests meeting the following criteria: 1. Bone marrow function: white blood cell count ≤ 30×10\^9/L; 2. Liver function: TBIL ≤ 1.5×ULN, TBIL ≤ 3×ULN if Gilbert's syndrome; ALT and AST ≤ 3 ×ULN; 3. Renal function: creatinine clearance rate (CCr) \> 50 mL/min calculated according to the Cockcroft-Gault method 4. Coagulation function: activated partial thromboplastin time (APTT) and prothrombin time (PT) ≤ 1.5×ULN. * 10\. The serum pregnancy test for female patients of childbearing potential should be negative during the screening period. Male and female patients of childbearing potential must agree to use effective methods of contraception from signing an informed consent form during the screening period, throughout the study and for 3 months after the last dose of the RJK-RT2831, including but not limited to: abstinence, vasectomy in males, female sterilization surgery, effective intrauterine contraceptive devices or condoms, and effective contraceptive medications.. Note: Women of non-childbearing potential include permanent infertility (hysterectomy, bilateral oophorectomy, or bilateral salpingectomy) and postmenopausal women. Exclusion Criteria: * 1\. APL is suspected or confirmed based on morphology, immunophenotyping, molecular testing, or chromosomal karyotyping, or other hematological tumors, such as myeloid sarcoma, mixed phenotype acute leukemia, accelerated phase and blast phase of chronic myeloid leukemia, etc.; * 2\. Has received any anticancer therapy or investigational drug within the following specified time period prior to the first dose of RJK-RT2831: 1. Received cytotoxic chemotherapy (except hydroxyurea use for subjects with leukocytosis \>10,000 cells/mm3 or rapid disease progression), radiotherapy (except local palliative radiotherapy), immunotherapy, targeted therapy and other anti-tumor treatments within 14 days; 2. Received adoptive cell therapy, such as autologous or donor natural killer cell or T lymphocyte infusions (e.g., chimeric antigen receptor-T cells), unless \> 60 days prior to the first dose of study treatment and treatment-related toxicities ha