Abstract： Objective To investigate the effect and the mechanism of different G-CSF-priming protocols on leukemia cell lines (HL-60 and U937) in vitro and provide the clinical guidance to clinical treatment of acute leukemia.Methods The leukemia cell lines HL-60 and U937 were used as model to detect the effects of three drugs alone and combined two drugs (HA) or three drugs (HAG) respectively.Cell viability and cell growth inhibition were performed by cell count kit-8 (CCK-8) assay.Apoptotic marker AnnexinV/PI,cell membrane surface antigen CD11b,cell cycle,mitochondrial membrane potential (JC-1) and Caspase-3 were determined by flow cytometry.Results After using of HAG for 48 h,HL-60 and U937 cells counts were decreased significantly and the apoptotic marker Annexin V was significantly increased. To compare the single drug group with two drug combination group,the result was significantly different (P ＜0.05),and the apoptosis of U937 cells was higher than HL-60 cell line.CD11b expression among the three groups did not change (P ＞ 0.05).Using of CAG and MAG,the mitochondrial nembrane potential of HL-60 and U937cells was increased,the three-drug combination group was significantly higher than single-drug group and control group (P ＜0.05); Caspase-3 was activated,the fluorescence intensities of Caspase-3 of the three-drug combination group and single drug group were significantly higher (P ＜0.05) comparing with the control group.Conclusion HAG regimen could induce leukemia cells to apoptosis through the reduction of mitochondrial membrane potential and the activation of Caspase-3 to induce apoptosis of leukemia cells.