Abstract: In this paper the synthetic fracture criteria has been applied to threedimensional medium. The conditions of the application of the synthetic fracture criteria to the crace extension under combined stress in three-dimensional have been given by the analysis and comparison of the theoretical solutious and the experimental results. The test results under mixed mode Ⅰ-Ⅱ, Ⅰ-Ⅲ and Ⅱ-Ⅲ fracture are compared with the theoretical curves predicted by four difterent fracture criteria.