Abstract: To study the height of water-conducting fracture zone of large mining length working face in deep coal mine, taking the 21106-working face of the Chengjiao Coal Mine in Yongcheng Mining Area as the engineering background, the drilling water injection and imaging method are used to test the height of water-conducting fracture zone, the UDEC software is used to explore the influence of coal seam burial depth and mining face length on the height of water-conducting fracture zone. The results show that the drilling water injection and imaging method test results are basically consistent, and the maximum of the height of water-conducting fracture zone is to be 49.20 m, and the ratio of fracture zone height to mining height is 17.14. It is larger than the calculation result of the “three down mining standards” formula, and is close to the calculation result of the Coal Mine Water Control Manual. As the length of the working face increases, the height of water-conducting fracture zone also increases, and the greater the burial depth, the greater the increase. When buried at a depth of 900 m, the height of water-conducting fracture zone in the 330 m mining length working face increases by 10.54% compared to the 160 m mining length working face. With the increase of buried depth, the height of water-conducting fracture zone also increases, and the larger the mining length, the greater the increase extent. When mining length is 330 m, height of water-conducting fracture zone under 900 m buried depth is 13.43% higher than that under 500 m buried depth. The error range in the “three down mining standards” and Coal Mine Prevention and Control Manual formula is relatively large, which makes it difficult to determine the specific height of water-conducting fracture zone. For the mine threatened by roof water damage, the field test method should be used to determine the water-conduction fracture zone height to provide the basis for the prevention and control of roof water damage.