The hypothetical surface protein LPL9_0968 in Lacticaseibacillus paracasei L9 was transcriptionally up-regulated 9.67-fold under bile salt stress. Through bioinformatics analysis， it was found that LPL9_0968 belongs to the surface protein of LiaX family， and the sequence similarity with LiaX protein in Enterococcus faecalis is as high as 61.96%， and there are multiple asparagine-glycine(NG) conserved sites in this family protein. Therefore， in this experiment， an inactivation mutant of the LPL9_0968 operon gene was constructed. Under 0.075% Ox-bile stress， the bile salt tolerance of the mutant was reduced by 10 times， indicating that the LiaX family protein is involved in the L9 bile salt stress resistance mechanism. Subsequently， the mutant strain exhibited strong sensitivity to glycine deoxycholate under single-component bile salt stress. Under the stress of 3.0% taurocholic acid， 0.4% taurodeoxycholic acid， 2.0% glycocholic acid， 0.075% glycodeoxycholic acid， the survival rate decreased by 1.95， 2.85， 2.05 times and 8.21 times， respectively. Furthermore， the results of Zeta potential experiment and scanning electron microscope showed that the cell membrane potential of the mutant strain increased under bile salt stress， and more severe atrophy appeared. Molecular docking showed that the surface protein interacted with different components of bile salt. Therefore， LPL9_0968 is likely to sense bile salt signaling molecules， regulate cell membrane surface proteins， and maintain the stability of cell membranes to improve the bile salt resistance of strains. This experiment explored the function of the surface proteins of the LiaX family in lactic acid bacteria for the first time， proved its importance in the bile salt stress resistance of the strain， and laid a theoretical foundation for the in-depth study of its anti-bile salt mechanism.