Abstract: S-N curves under different test conditions were obtained through rotating bending fatigue test and axial fatigue test methods, and the effects of different loading frequencies and stress ratios on the fatigue performance of 18CrNiMo7-6 alloy steel were studied. The fracture surface of the specimens were observed by SEM. The results show that there is frequency effect under normal loading frequency, as the loading frequency increases, the fatigue strength of 18CrNiMo7-6 alloy steel increases, and the yield strength gradually increases with the increase of the strain rate. It is found that there is no obvious difference in the fracture mechanism under different loading frequency. When the maximum stress is the same, the fatigue life of 18CrNiMo7-6 alloy steel increases with the increase of stress ratio. The fatigue life of 18CrNiMo7-6 alloy steel under different stress ratio is calculated by using the finite element method combined with the BrownMiller model, which is in good agreement with the test results.