In shot peening process the work piece surface is struck by a large number of balls and compressive residual stress is generated on the surface. So, mechanical properties such as fatigue strength, stress corrosion resistance, smooth shape and ... will improve. In this paper, the balls with a speed of 100 to 200 m/s were struck on the steel samples and fatigue strength compared with specimens without shot peening. The results indicated a significant increase in fatigue strength. Also the balls deep changes on the samples were calculated using ANSYS software and the results were compared with the experimental results. Results showed that, if the ball speed is 100 m/s, it leads 25% increase in fatigue strength while the residual stress will increase to 250 MPa. Furthermore, if the ball speed is 200 m/s, fatigue strength and residual stress increase up to 40% and 300 MPa, respectively. It is also concluded that the stress in the balls is twice as the work piece surface residual stress. تفاصيل المقالة