Abstract: In order to explore the feasibility of the technology of increasing permeability of coal seam caused by liquid nitrogen, the theory of the technology is analyzed, and the effect of ultra-low temperature of liquid nitrogen on the porosity and permeability of coal body is studied by the method of experimental test.The results show that the effect of ultra-low temperature of liquid nitrogen makes the internal temperature of coal sample suddenly reduce, and the stress produced by ultra-low temperature of liquid nitrogen has exceeded the tensile stress the permeability and porosity of coal samples increased by more than 2 times and nearly 1.5 times, respectively.When the time of ultra-low temperature action of liquid nitrogen exceeded a certain threshold, the trend of increase of the two values slow down.Combined with the theory of thermodynamics and fracture mechanics, the mathematical and physical model of coal temperature distribution under the action of liquid nitrogen at ultra-low temperature is constructed, and the analytical solution of coal temperature field and stress field under the action of liquid nitrogen is obtained, and the mechanism of liquid nitrogen on the development and development of coal fracture is explained.