Abstract: The four-point bending fatigue test method was used to test the fatigue properties of 4330 steel samples processed by laser shock peening. The improvement mechanism of fatigue performance of 4330 steel was studied by microscopic hardness meter, scanning electron microscope, X-ray residual stress tester and electropolishing tester. The results show that fatigue fracture occurs in an average of 328, 400 cycles of untreated samples, but after laser shock peening treatment,the cycles still intact for 1 million times, the fatigue life is at least 3.05 times than that of the untreated samples, and the residual compressive stress depth could reach more than 1.5 mm, and the surface microhardness increases by 18.9%. The initiation of crack source of 4330 steel samples can be promoted to a certain depth below the surface by laser shock peening.