The antibacterial effects of complex preservative of sorbate, sodium diacetate and sodium erythorbate on Staphylococcus saprophyticus in shrimps were investigated in this study. To determine the minimum inhibitory concentration of compound preservative on tested strain by ELISA method (MIC), and determination of antimicrobial activity, bacterial growth curve, cell membrane integrity, alkaline phosphatase (AKP) levels and other indicators, combined with the observation of ultrastructure of bacteria, were used to evaluate the antibacterial influence of composite preservative on the S. saprophyticus. The results showed that the complex preservative can significantly reduce the growth rate of S. saprophyticus, its MIC is 109 μg/mL, the minimum bactericidal concentration (MBC) of 219 μg/mL, antimicrobial activity at the initial stage of use (around 3 h) was the strongest. The amount of alkaline phosphatase in bacterial solution significantly increased with the prolongation of time, and the absorbance at 260 nm was significantly increased. It indicated that the bacterial DNA and protein leakage, cell wall and cell membrane was destroyed. Scanning electron microscopy showed that the dry rupture occurred for the experimental group, as well as rupture of cell wall and cytoplasm from the cell exudation. The compound preservative agent of certain concentration had inhibitory (killing) effect on S. saprophyticus in shrimps and showed certain destructive effect to the cell.