Abstract: In order to study the problem of retaining water proof coal and rock pillars under the condi‐ tion of gully mining in loess gully area，taking the 200 working face of Shuanglong Coal Mine as an exam‐ ple，according to the structural and hydrogeological characteristics of overlying strata in coal mines，the de‐ velopment height of water-conducting fracture zone and the failure law of overlying strata under mining con‐ ditions are analyzed by engineering geological analogy method and numerical simulation method. The results show that the crack-mining ratio of 200 working face is determined to be 28 by engineering geological analo‐ gy method，and the development height of water-conducting fracture zone is 50.40~89.60 m. By analyzing the range of plastic failure zone and vertical displacement of overlying rock after mining influence，when the working face continues to advance to 500 m，the overlying rock of coal seam roof has been completely de‐ stroyed，and the height range is 51.2~95.8 m. The development height of water-conducting fracture zone is closely related to the buried depth and thickness of coal seam in working face. When the height of waterproof coal pillar in Quaternary aquifer of 200 fully mechanized mining face is 58~110 m，it meets the require‐ ments of ditch mining. The field practice shows that after the mining of the working face，the water of the Wangcungou river is not introduced into the working face，and the safe mining and water-preserved mining are realized. The research results can provide reference for coal mining in loess gully region.

Key words: ditch mining, waterproof coal and rock pillar, engineering geological analogy method, plastic failure zone