Abstract: In order to solve problem of high-seam mining under Changlong reservoir with fully-mechanized mining in Zhangcun Coal Mine at Lu'an Minefield，the developing rule of water flowing fractured zone was studied by way of field measurement and engineering analogy.Analysis on safety mining under reservoir was done by calculating height of waterproof pillar.The size of pillar to prevent normal fault of South of Wenwangshan was designed，and influence of the fault on mining under water was analyzed.Mining subsidence was predicted with probability integral method，and Kriging Analysis was applied to define the reservoir inundated area.The limit depth of mining ground fissure was predicted based on in-site critical value of ground horizontal deformation，and by which mining influence on dam and leakage in reservoir area was analyzed.It was stated that height of water proof pillar was enough for mining under reservoir，and safety technical measures could be well used.The extent of reservoir inundation increased.The limit depth of mining ground fissure was about 7.8 meters，and leakage and rapid drawdown of water level of reservoir won't happen.It is safe to mining under Changlong Reservoir，and the ground water resource was protected at the same time.