The paper focuses on the research on the stability of goaf roof with different water content by FLAC3D software.Roof span is the most dominative factor affecting the stability,so four span valves are used here.The maximum of vertical displacement was taken to evaluate the roof stability.The test results prove that there is a critical value on roof stability caused by water content.Rocks' density and strength are different in different water content conditions.The maximum ground surface vertical displacement...