Effects of laser shock processing (LSP) on cavitation erosion behaviors of ANSI 304 stainless steel thick sheets treated by laser welding are investigated. Mechanical properties and microstructure of laser weldments are measured and observed by X-ray diffraction (XRD), microhardness, electronic balance and scanning electron microscope (SEM) tests in order to investigate cavitation erosion resistance of laser weldments. Results show that with the increment of LSP pulse energies after cavitation erosion, the martensite intensity is improved relatively and the removal of martensite is restrained, the hardness increases, and the cumulative mass loss and damaged surface areas of laser weldments decrease. Meanwhile, the martensite grains are fined, and undulations and upheavals become shallower and sparser, and the growth and propagation of the cracks on the surface are restrained. Thus, cavitation erosion resistance of laser weldments is enhanced. In addition, cavitation erosion resistance of laser welding zone (LWZ) is better than that of heat-affected zone (HAZ).