According to the study of multiaxial fatigue life of 30CrMnSiA steel, the concept of equivalent S-N curve is proposed based on the uniaxial tension-compression and pure torsion S-N curves in this paper. Based on the equivalent S-N curves, an empirical formula is established to predict the multiaxial fatigue life of hard metal materials. The empirical formula is verified by predicting the fatigue life of various hard metal materials in the literature. Results show that more than 94.0% of the data points are in the ±3 times fatigue life scatter band, and more than 81.8% of the data points are in the ±2 times fatigue life scatter band.