Abstract: Objective: To establish a constant model of malignant tumor cell differentiation and to set up a set of methods that the differentiated cells can be identified.Methods: HL-60 cells influenced by all-trans retinoic acid(ATRA) capable of inducing differentiation at different time were used as subjects.The differentiation marker on the cell surface and the cell volume were analyzed by using flow cytometry.The differentiated cells were identified by confocal microscope after having been stained with PI.Results: With the drug-inducing time increasing,the volume of differentiated cells was enlarged gradually.After 72 hours,the differentiated cells induced by ATRA began to express differentiating marker CD11b and the differentiated cells,nuclei was changed into the nucleus morph differentiation just like nutrophil nuclei.Conclusions: The differentiation of HL-60 cells can be induced by ATRA.HL-60 cells,differentiation can be conveniently judged by combining the cell svolume,and the cells differentiating marker,analyzed by flow cytometry with morphodifferentiation observed by confocal microscope after having been stained with propidium iodide.