Based on the study of multiaxial fatigue life of 30CrMnSiA steel, the concept of equivalent S-N curve is proposed in this paper. Based on the equivalent S-N curves, an empirical formula for predicting multiaxial fatigue life of hard metal materials is established. The empirical formula is simple and convenient for engineering application. In addition, the empirical formula is used to predict the multiaxial fatigue life of various hard metal materials in the literature. Results show that more than 94% of the data points are in the ±3 times fatigue life scatter band, and more than 81% of the data points are in the ±2 times fatigue life scatter band.