Abstract: In order to solve the problem of safety coal pillar design，which under the gravel aquifer of Neogene in Zhaojiazhai coal mine，the geological situation of loose seam and hydrological of 12 mining zone were evaluated，waterproof coal and rock pillar should be set for working face in 12 mining zone according the results，the development height of diversion fissure zone that appeared during coal mining process was simulated by UDEC，the diversion fissure zone height was predicted by the optimal formula of full-mechanize caving mining，and protective layer thickness was selected by method of ‘the minimum and effective waterproof thickness’，and worked out the height of waterproof pillar at the end.The results showed that waterproof pillar height were 95.42m，112.93m and 86.56m of 12205，12211 and 12201 working face，respectively，the safety of waterproof pillar was verified by success mining of 12211 working face.