Abstract: As a type of gear contact failure, compared with pitting, micro-pitting, and scuffing which show indications on the tooth surface, tooth flank fracture has more latent danger. In order to study the mechanism, influence factors, and etc. of the tooth flank fracture, a predictive method based upon the local strength concept was introduced. Discussions were made in the work of the failure characteristics and form mechanism of tooth flank fracture. In addition, important influence factors of the tooth flank fracture such as residual stress were discussed. The prediction and calculation methods of the tooth flank fracture were studied in this paper. The research provides theoretical support for both the further analysis and the gear design against tooth flank fracture.