Abstract: The confining pressure effect of the shear strength of frozen soil is the basis and prerequisite for analysing the bearing capacity of engineering construction in cold regions and the engineering project constructed by the artificial freezing method. As the confining pressure increases, the existing test results of shear strength of the frozen soils show both a two-stage law that increases first and then decreases, and a three-stage law that increases first, then decreases and then increases again. In order to characterize the special development of the shear strength of frozen soils, properties of soils and ice are analysed. It is believed that the shear strength of frozen soil presents a multi-stage development, not only because it inherits the strength characteristics of the soil, but also because the existence of pore ice makes a special contribution to shear strength. On the basis of the above analysis, the shear strength of frozen soil is decomposed into the base strength reflecting the cohesive-friction properties and the special contribution strength of pore ice to the shear strength of frozen soil. By adopting the power function strength expression as the base strength of frozen soil, and further establishing the contributed strength describing the strengthening and weakening rules of frozen soil, a three-stage strength criterion incorporating the confining pressure effect is developed for frozen soils. The comparison between the test results of frozen soils in different types and the predictions shows that the established strength criterion is capable of capturing the variation rule of shear strength of frozen soils.