Objective To investigate the diagnostic value of immunophenotype in distinguishing acute promyelocytic leukemia(APL)from HLA-DR negative acute myeloid leukemia(AML)using flow cytometry.Methods A retrospective observational study was con-ducted including 42 APL patients and 28 newly diagnosed or relapsed HLA-DR negative AML patients admitted to our hospital from 2014 to 2024.Immunophenotype analysis was performed on bone marrow aspirate samples using flow cytometry.The positive expression rates of CD64,MPO,CD7,CD11c,CD9,CD123 and other antigens were compared between the two groups using the Chi-square test.The diagnostic efficiency of the CD9/123 and CD64+MPO+CD7 CD11c-models for APL was evaluated using receiver operating charac-teristic(ROC)curves.Results The HLA-DR negative AML group exhibited significantly lower positive rates of CD64,CD9 and MPO(P＜0.05),and higher positive rates of CD11c and CD7(P＜0.05)compared to APL group.The CD64+MPO+CD7-CD11c-model had an area under the curve(AUCROC)of 0.859,sensitivity of 93.8％and specificity of 75.0％for distinguishing APL.The CD9/CD123 expression pattern had AUCROC of 0.919,sensitivity of 83.3％and specificity of 84.0％for APL diagnosis.The combined CD9/123 and CD64+MPO+CD7-CD11c-model had AUCROC of 0.955,sensitivity of 83.3％and specificity of 100％.Conclusion The combined CD9/123 and CD64+MPO+CD7-CD11c-expression pattern may serve as a helpful tool for differentiating APL from HLA-DR negative AML.