Abstract: The research on microcosmic characteristics evolution of the cement improved frozen soil under thawing compression is of great significance to understand the process of the improvement. In this study, Thawing compression test is conducted with the cement treated frozen soil. The specimens of SEM are prepared with the method of freezing- drying and the microscopic characteristic images are obtained. The real three-dimensional pore ratio is obtained by the specific gravity test. The gray value is selected for image segmentation as the reference of the real pore ratio and the microscopic pore characteristic is extracted. Based on the results of the compression test, the pore characteristics, such as the diameter, quantity, area, directional angle and abundance, are quantitatively analyzed. The results show that the strength of macropore structures is enhanced when the frozen soil is improved by cement, causing an increasing pore ratio and pore area, and a decreasing compression. With the development of the compression, the orientation angle distribution of the pores transfers from the originally uniform style to the serrated style. The pores tend to be elongated with the compaction of the pores with the abundance value greater than 0.5 while the whole pore abundances tend gradually to be normal distribution. The research on microstructure evolution provides a scientific basis for interpreting the mechanism of the enhancement on the macroscopic mechanical properties of the cement improved frozen soil.