The purpose of this study was to verify whether nicotinamide mononucleotide (NMN) and metformin (MET) can promote the proliferation of natural killer cells (NK cells) and improve the anticidal function.The method used in this study was to add different concentrations of NMN or MET into the NK cell expansion system to analyze its effect on cell proliferation,and to detect its cell phenotype,apoptosis ratio,cell cycle,cell fragility and tumor killing ability by flow cytometry.The results of this study were that the final concentration of 0.5 ng/mL NMN,10 mg/mL MET or 0.5 ng/mL NMN+10 mg/mL MET was added to the NK cell expansion system through pre-experiment.On the 7th day,cell count showed that the number of cells in all experimental groups increased significantly compared with the control group (P<0.05),and there were no significant differences in CD3^-CD56⁺CD16⁺ cells,apoptosis and cell cycle among all groups on the 7th day (P>0.05). On the 14th day,the total number of cells in the experimental group was significantly higher than that in the control group,and the total number of CD3^-CD56⁺CD16⁺ cells in the MET group and the NMN+MET group was significantly higher than that in the control group (P<0.05),but there was no significant difference in apoptosis ratio and cell cycle between the two groups (P>0.05).The cell fragility test on the 14th day showed that the total number of surviving cells in NMN,MET and NMN+MET groups was significantly higher than that in control group (P<0.05).The tumor killing experiment on the 14th day showed that NMN and MET could significantly inhibit the growth of tumor cells (P<0.05).Research has found that NMN and MET can effectively promote the proliferation of NK cells,while reduce the brittleness of the cell membrane; NMN and MET can promote the proliferation, but do not cause the increase of apoptosis and the significant change of cell cycle,and show significantly increased tumor killing activity.