Abstract: The content and distribution characteristics of unfrozen water in the pores of coal seams can reflect the degree of coal thawing. The degree of coal thawing affects the size of ice pores, directly determines the pore permeability and affects the efficiency of coalbed methane extraction. It is of great significance to study the ice-water phase transformation characteristics in coal under freezing conditions for accurately evaluating the efficiency of cryogenic fracturing technology. Taking the frozen saturated bituminous coal as the research object, the nuclear magnetic resonance technology was used to study the pore characteristics of coal samples during thawing process. The pore structure was comprehensively analyzed by measuring T₂ curve, cumulative porosity and cumulative pore throat distribution. The results show that in the thawing process of liquid nitrogen cyclic frozen coal, the micropore structure is thawed first, and then the mesopore and macropore structures are thawed, and the pore connectivity is poor in the early thawing stage. By calculating the area of T₂ curve, the exponential relationship between unfrozen water content and temperature was verified, and the fitting curve was established. Simultaneously, the thawing process of coal samples was divided into three stages according to the cumulative porosity and pore throat distribution, which were the accelerated thawing stage(-196--30 ℃),the normal thawing stage(-30--5 ℃) and the rapid thawing stage(-5-10 ℃). Thermodynamic analysis shows that the unfrozen water content of coal samples at low temperature is affected by both pore pressure and pore size distribution, that is, the higher the pore pressure and the richer the micropore structure, the higher the unfrozen water content of coal samples. The analysis system of pore expansion and contraction and local thermal conductivity characteristics based on liquid nitrogen cycle freeze-thaw technology was summarized, involving key issues such as the analysis of T₂ spectrum, the division of thermal conductivity components, and the calculation of thawing speed. The differences in the thawing speeds of coal samples caused by different liquid nitrogen cycles were analyzed. The calculation results show that the average thawing speed of coal sample was the fastest when the liquid nitrogen frozen for 10 times. The maximum thawing speed of ice in micropore, mesopore and macropore were 0.632%/℃,0.582%/℃ and 0.521%/℃,respectively.