Abstract: 300M steel was strengthened using two kinds of high intensity shot peening process in different intensities of 0.424 mm and 0.576 mm,the strengthening effects were investigated through surface integrity,residual stress field,microhardness and fatigue resistance. Results show that the shot peening surface of 300M steel was completely covered by craters,and the surface roughness raised significantly after shot peening treatment. High strength residual compressive stress fields formed in the sample surfaces,and their microhardness was enhanced. The fatigue life after shot peening increased slightly compared with that before shot peening. The stress concentration caused by high surface roughness and the appearance of microcracks could be used to explain that fatigue life did not increase significantly.