Abstract: In order to investigate the effects of the coal ranks on fracturing low-permeability coal bed through liquid nitrogen cooling, the meta anthracite and the m edium coking coal were obtained and immersed in liquid nitrogen.The wave velocities before and after liquid nitrogen cooling were measured by ultrasonic tester.The eff ects of coal ranks and saturation on liquid nitrogen fracturing coal samples are investigated.The results show that: after the saturation, the wave velocity of the anthracit e decreases, and the wave velocity of the coking coal increases.For dried coal samples, after liquid nitrogen cooling the damage of the anthracite is more serious than t hat of the coking coal. Saturated coal samples after liquid nitrogen cooling are much effectively damaged and fractured.The average wave velocity of the saturated anthr acite samples and coking coal samples after liquid nitrogen cooling decreased by about 19.8% and 27 .6%, respectively.The damages of the later are much more signific ant.