According to the microwave radiation characteristics, this paper introduced a new frozen soil dielectric model to calculate the dielectric constant of frozen and thawed soil based on the Helsinki University of Technology (HUT) microwave snow emission model. The Advanced Integrated Emission Model (AIEM) was used to calculate surface emissivity. The multi-frequency microwave radiation model and soil freeze/thaw discriminant algorithm were improved. The classification accuracies of original and improved soil freeze/thaw discriminant algorithms were validated using AMSR2 Level 3 daily gridded 0.25° brightness temperature products and the measured values obtained by ground-based microwave radiometer. The results showed that compared to the original discriminant algorithm, the frozen soil classification accuracy of the improved discriminant algorithm was effectively improved and the overall classification accuracy reached 82%. It turned out to be a comparatively reliable mode of discrimination.