【Objective】 Freeze-thaw action will change the microstructure of a soil, and the change in pore characteristics is an important reflection of the change in soil structure. Most of the regions along the mid-latitudes on earth are affected by seasonal freeze-thaw processes, especially the black soil in Northeast China. It is of great significance to study mechanism of the erosion on black soil and rational utilization of the black soil resources. So this study is oriented to analyze three-dimensional structure of the soil under freeze-thaw condition, extract quantitative indices of pore characteristics, and then explore effects of freeze-thaw cycle on soil macropores, in an attempt to provide evidence for further revealing influences of seasonal freezing and thawing on soil structure of the black soil area. 【Method】 In this paper, through indoor simulation experiment of freeze-thaw cycle and with the aid of the CT scanning technique, changes in macropore in the undisturbed black soil samples under different numbers of freeze-thaw cycles and different moisture contents were studied. Undisturbed soil samples, 0～15 cm in depth, were collected with PVC pipe from a typical black soil area for the indoor simulation experiment of freeze-thaw cycle, which was designed to have two moisture contents (30% and 40%), and seven levels of freeze-thaw cycles (0, 1, 3, 5, 7, 10 and 15), each ranging in temperature from -10 to 7°C. With the aid of a medical CT, 1.25 mm in resolution, changes in pores > 1.25 mm in pore size were studied. 【Result】 Results show that with the increasing number of freeze-thaw cycles, soil porosity continuously increased, especially after the 7th freeze-thaw cycles, while the number of pores decreases; regular porosity (RP) and irregular porosity (IRP) continued to decrease, but lengthening porosity (EP) increased; and pore size increased, especially that of those >3 mm in diameter. Besides, freeze-thaw action caused formation of a lot of branches along pores, and the more the numbers of freeze-thaw cycles, the higher the proportion of branches. Among the soil samples subjected to the same temperature variation in freeze-thaw cycles, those high in soil moisture content changed more significantly in pore characteristics than those low in soil moisture content. 【Conclusion】 As affected by freeze-thaw cycle, soil porosity, pore size and pore branching increased, and soil pores changed significantly in shape and distribution. All the findings in this study show that the number of freeze-thaw cycles and soil moisture content are the two major factors affecting pore structure of the soil. Properties of the soils under freeze-thaw cycle is not only a very important research hotspot, but also a major factor concerning sustainable development of the agriculture in Northeast China. In order to reveal mechanism of freeze-thaw erosion of the soil, further study should be done focusing on pore structure characteristics of aggregates and relationships between pore structure characteristics and soil water-holding and infiltration characteristics in the soil under freeze-thaw cycle. The study may provide a theoretical basis for researches on mechanism of freeze-thaw erosion of soil and reasonable evaluation and utilization of farmlands in cold-temperate areas.