In order to improve the anti cracking performance of asphalt stabilized macadam, the gradation of asphalt stabilized macadam was optimally designed with coarse aggregate gapped and semi opened gradation(ATB 25). Double sides shear fatigue tests under different stress ratio, namely 01, 02, 03, 04, 05 were carried out on ATB 25 beam samples. It is found that the stress ratio has a significant effect on the fatigue life, and the fatigue life under different stress ratios are all subject to the double parameter Weibull distribution, and the p S N type shear fatigue equations with different failure probability are established.