With the rapid development of deep mining engineering, the failure mode and strength of rock under high stress are obviously different from those under shallow buried conditions.In this process, a variety of failure mechanisms such as rock elongation, shear and compaction yield coexist.In view of the above problems, based on the maximum linear strain theory and PMC transition criterion, this paper puts forward the strength theory suitable for the transition characteristics of failure modes of deep rock mass, reveals the internal mechanism of low-strength failure of rock mass, and puts forward the inequality unified form of strength criterion under the influence of multiple failure mechanisms with generalized shear stress, average stress and stress Lode angle as parameters.At the same time, the PMC strength model with multiple failure mechanism is used to fit the test data of sandstone and granite, and the obvious segmented strength characteristics of rock are obtained.The research results show that the rock strength exhibits obvious segmental strength characteristics, which conforms to the strength law under the influence of multiple failure mechanisms.The applicability of PMC strength model with multiple failure mechanisms to rock materials is verified.