Abstract: In order to determine the upper mining limit reasonably，according to the current drilling data and supplementary exploration data for hydrogeology in Luxi Coal Mine，a comprehensive analysis of the Quaternary lower water-resisting layer，the thickness of bedrock，rock mechanical parameters of rock and rock wind oxidized zone condition was made.Then compared the height of water conducting fracture zone from the measured data of Luxi Coal Mine，the empirical formula of “three-underground” procedures and the empirical formula under thin bedrock of Xinglongzhuang Coal Mine，the empirical formula of “three-underground” procedures was adopted to predict the crack height of overburden rock fracture zones after mining in the 3111II working face，obtaining strata lithology as “medium hard” and the mean square error 0.The conclusion was drawn that only lower part of No.3 coal layer in bifurcation area was determined to be explored with the height of waterproof coal/rock pillar of 38 m，and No.3 coal layer in the combined area was explored by two sub-levels with height of waterproof coal/rock pillar of 49 m.

Key words: Water conducting fracture zone, The upper mining limit, Waterproof coal/rock pillar, Empirical formula, Feasibility study