Abstract: Filter paper diffusion method was used to study the bacteriostatic activity of ethanol extracts from water chestnut stem and water chestnut pericarp and their different solvent extracts. The effects of different temperature,pH and UV irradiation on the stability of bacteriostatic activity of ethyl acetate extracts from water chestnut stem and water chestnut pericarp were also investigated. Finally,the components of ethyl acetate extracts from water chestnut stem and water chestnut pericarp was studied by HPLC and HPLC-MS to identify. The results showed that the minimum inhibitory concentrations of the extracts of water chestnut stem and water chestnut pericarp to Staphylococcus aureus,Escherichia coli and Saccharomyces cerevisiae were 0.391,0.391,3.125 mg/mL and 0.098,0.195 and 1.563 mg/mL,respectively,the antibacterial effect showed that the ethyl acetate extract of the water chestnut pericarp was superior to the ethyl acetate extract of the water chestnut stem. Both extracts had a significant bacteriostatic effect on Gram-positive bacteria,and the effect was stronger than Gram-negative bacteria,and they had the weakest antibacterial effect on fungi. The ethyl acetate extracts of water chestnut stem and water chestnut pericarp showed good antibacterial stability when treated at 20~100 ℃,pH5~9 and ultraviolet light for 10~40 min. The content of gallic acid and 1,2,6-tri-O-galloyl-β-D-glucose in the ethyl acetate extract of water chestnut stem was 45.87%. The content of 1,2,3,6-tetra-O-galloyl-β-D-glucose,Quercetin-3-O-galactoside and 1,2,6-tri-O-galloyl-β-D-glucose in the ethyl acetate extract of water chestnut pericarp was 57.84%. This paper provides a reference for the practical application of the extracts of water chestnut stem and water chestnut pericarp as bacteriostatic agents.