To explore the method for quantitative determination of active constituent in Sophora alopecuroides L. and its anti-cancer activity. Method for quantitative determination of matrine in Sophora alopecuroides L. is established using HPLC with CLC-phenyl column, mobile phase of acetonitrile-anhydrous ethanol-3% phosphoric acid solution (80:10:10), detection wavelength of 220 nm and flow rate of 1.0 mL·min-1. Breast cancer MCF-7 cells are cultured by routine method. Inhibitory effect of matrine on breast cancer MCF-7 cell proliferation is determined by MTT assay. Flow cytometry is used to analyze the changes in cell cycle after treatment, and record percentages of Bax and Bcl-2 positive cells. 48 h after treatment with test concentrations of matrine, cell cycle of MCF-7 cells are evidently altered. With the addition of matrine, S phase MCF-7 cells are markedly reduced, and G0/G1 phase cells markedly increase, while G2/M phase cells do not change much. Flow cytometry results show that the test concentrations of matrine can effectively inhibit the viability of MCF-7 cells, and promote their apoptosis. Different concentrations of matrine can all somewhat increase the positive rate of Bax expression, and the effect exhibits an increasing trend with increasing concentration. Bcl-2 expressions of treatment groups are all evidently lower than the control group, showing a negative correlation. HPLC method is reliable and accurate in determining alkaloids in Sophora alopecuroides L., and matrine in Sophora alopecuroides L. can effectively inhibit the proliferation of breast cancer MCF-7 cells.