Objective To investigate the effect of phenformin combined with hexokinase inhibitor 2-deoxyglucose (2-DG) on the treatment of triple-negative breast cancer cell lines 4T1 and MDA-MB-231. Methods Following treatment with phenformin, 2-DG or phenformin combined with 2-DG on 4T1 and MDA-MB-231 cells for 48 h, the cell proliferation in each group was detected by SRB and the apoptosis of cells was detected by flow cytometry. The concentration of glucose and lactic acid in cell culture supernatant was detected by ELISA. The activity of mitochondrial respiratory chain complex Ⅰ was detected by FlexStation3 and the mitochondrial oxygen consumption (OCR) was assayed with the Seahorse X Fe Analyzer. Results The hexokinase expression (4.6±0.17,3.73±0.21), glucose consumption (356±31，397±42) μg/10⁵ cells , Lactic acid concentration (5.59±0.52, 7.83±0.78) μmol/L in the supernatant of 4T1 and MDA-MB-231 cells in Phenformin group were higher than that in control group ( 1±0.15，1±0.12 ) , ( 289±25，301±32) μg/10⁵cells , ( 2.37±0.18，4.01±0.45) μmol/L (P < 0.01). Even if the dose was reduced by 90%, the cell viability of phenformin combined with 2-DG group (64.63±2.28, 51.97±2.29) % was still higher than that of phenformin group (86.70±1.83, 85.53±1.46) % (P<0.001). The combination of the two drugs significantly promoted the apoptosis of 4T1 and MDA-MB-231. In addition, compared with the phenformin group (5.59±0.52, 7.83±0.78) μmol/L, the phenformin combined with 2-DG group (3.46±0.37, 5.18±0.62) μmol/L cell lactic acid production also greatly reduced (P<0.01). Compared with the phenformin or 2-DG single-drug group, the phenformin combined with 2-DG group can significantly inhibit the growth rate of tumors in tumor-bearing mice (P<0.01). The median survival time of tumor-bearing mice in the phenformin combined with 2-DG group was 72.5 d, which was higher than that in the phenformin group 57 d and 2-DG group 55.5 d (P<0.01). Conclusion Hexokinase inhibitor 2-DG significantly enhances the therapeutic effects of phenformin on triple-negative breast cancer cells.