A simple method for measuring S-N curve and fatigue limit of a material or a machine part was detailed by a experiential fatigue strength decreasing model in this paper. According to experimental fatigue life of one point stress and static strength, the S-N curve of a material or a machine part was calculated by fatigue strength decreasing model. This new measurement method was validated with different kinds of parts. Upon strength decreasing model, the S-N curve and critical load of two materials were acquired with much less samples than before. The results showed that fatigue strength decreasing model and S-N curve measurement method were feasible and usable.