Cracks were prefabricated on compact tension specimen of 7050 Aluminum alloy, which was laser shock processing(LSP) once and three times. The whole crack initiation process, distribution and size evolution on aluminum alloy was studied with replica technique and through optical microscope. It was found that without LSP, small cracks initiated at the grain boundary and grew quickly. The cracks continued growing in depth. The growth of short cracks had the trend of stop-and-go oscillation, the crack data were relatively scattered, and short cracks had short average length and grew earlier. After LSP, surface residual compressive stress restrained to the trend of crack origins where crack origins would form most easily; after origination, cracks initiated towards the processed region, but stop temporarily if encountering great resistance, and might generate additional crack origins; Moreover, the higher the level of stress created by LSP was, the fewer cracks initiated.