In order to analyze the influence of liquid nitrogen immersion on the fatigue crack extension in water cut coal seam, dry coal samples, 50% water saturated coal samples and 100% water saturated coal samples were collected respectively, and a cyclic fatigue liquid nitrogen immersion experiment was carried out in laboratory. The changes of crack structure on coal sample surface before and after liquid nitrogen immersion was observed by laser microscope and the crack extension velocity was measured by sound wave tester. Results show that 1)liquid nitrogen immersion has no obvious effect on the dry coal samples, which were still intact after 10 immersion cycles; 2)the crack extension is mainly along the vertical direction to joint;3)the higher the water saturated degree is, the more obvious the crack extension of coal sample; 4) the higher the water saturated degree is, the shorter the immersion period required by liquid nitrogen immersion. The water saturation percentage of coal specimen has remarkable effect on the coal crack growth due to liquid nitrogen immersion.