Abstract: The submerged water jet was adopted to strengthen 45 steel.The surface of the sample was measured by microXAM Three Optical-profile.The microscopic construction was observed by S-3000N Scanning Electron Microscope.The change of hardness was measured by 71 microhardness instrument.The result shows that the surface strengthening effect is obviously after water jet cavitation shot penning impacted on the 45 steel surface,jet time and jet pressure has marked influence on the ability of water jet cavitation.The surface quality introduced by water jet cavitation shot peening is higher than that introduced by traditional shot peening.