Abstract: High power density(GW/cm2)short pulse(ns) laser was used for laser shock processing(LSP)45 carbon steel.The effect of LSP on the microstructure and structural changes of 45 carbon steel was studied.The fatigue fracture shapes of unshocked section and shocked section of the sample were examined with the scanning electron microscope(SEM).The experimental results show that laser shock processing can make the fatigue crack of 45 carbon steel not easy to initiate and propagate.The fatigue life of 45 carbon steel was significantly increased.