Abstract: The shot-peening and the fatigue tests of 40Cr, 20Cr and 30CrMo steels are conducted. The residual stress field and the surface roughness parameters are measured. The culculating model and the modified Goodman equation for the fatigue limit with surface fatigue sources are established. According to the internal fatigue sources, a new concept of internal fatigue limit(IFL)and relevant strengthening mechauism are developed. IFL is always bigger than the surface fatigue limit (SFL). It is found that the following proportional relation between IFL and SFL exists; IFL/SFL- 1.34. On the basis of the study mentioned above, the comprehensive effects theory for shot-peening strengthening is put forward.

Key words: shot-peening, rebidual stresses, fatigue strength, internal fatigue limit