In order to study roof breaking law of unstable layer spacing in mining thin coal seam, 8411 working face in Yungang Mine was taken as engineering background in this paper, some measures like mechanical structure theoretical analysis, numerical simulation and perform inspection were adopted. Researches indicated that unstable distance coal seam mining in thin seam roof broke in granular media damaged structures, instability of the loose rock blocks happened to slip. The numerical simulation results showed that roof strength was low without supporting, with the advance of the working face, roof continued falling, ground pressure appeared weak. According to date of rock pressure law from field collected, first roof weighting interval in working face was 25.5 m, periodic weighting distance was 21m, the variation law of ore pressure was consistent with the numerical simulation results.