Abstract: The paper used methods of field strata control observation and RFPA numerical simulation to analyze and study ground behavior regularity of fully mechanized face with extra thick coal seam of easy spontaneous combustion in Gengcun Coal Mine. The results showed that there is acute ground behavior in 12170 fully mechanized face of Gengcun Coal Mine and obvious phenomenon of periodic loading in main roof whose average interval was 16.06 m; in whole range of fully mechanized face, phenomenon of periodic loading in main roof has obvious variance, namely loading strength is large in middle-lower and lower areas while small in upper and middle-upper areas; hydraulic supports have enough supporting resistance and high reliability in stoping process, which can satisfy requirements of fully mechanized caving of 2-3 extra thick coal seam; the result of RFPA numerical simulation is consistent with the one of field strata control observation, which showed validity of the method of RFPA numerical simulation about analyzing strata behavior regularity.