In order to study ranges of overburden fractures with different mining ratios， the method that combining theoretical calculation with numerical simulation experiment was adopted to analyze range of fracture zones after mining. Theoretical analysis was used to analyze range of fracture zones when fully mechanized mining height was 8m， and the range was about 53.8~100 m. UDEC numerical simulation method was used to experimentally analyze the fracture zone range at different mining ratios， the simulation result showed that the fracture zone height was inside range of numerical calculation. With increasing mining ratios， the crack range was gradually decreased. Finally， based on mine specific production conditions， ratio of mining was determined as 1∶1， which meant mining was 4 m and discharging was 4 m.