To establish a strength criterion that can consider the composite properties and internal non-homogeneity of frozen soil, a load sharing model is first defined based on homogenization theory and the binary-medium structure model, and then the strength functions of frozen soil on the p-q plane and the π plane are established, respectively. Finally, a three-dimensional nonlinear unified strength criterion for frozen soil is proposed. The applicability of the proposed strength criterion is verified based on the multi-group triaxial compression test results and the directional shear test results at different stress Lode angles.