Abstract: Taking No.12051 fully-mechanized coal face of Zhaogu No.1 Coal Mine as research object, thin bedrock deformation and strata behavior in coal seam mining under ultra-thick unconsolidated strata were studied by use of UDEC numerical simulation software. The results show that the first weighting interval and periodical weighting interval of the coal face is 55 m and 15 m respectively. Caving zone and fractured zone appear in overlying strata after mining. The height of caving zone and fractured zone is 12.4 m and 36.7 m respectively. Ratio of caving zone height to mining height is 3.54 and ratio of fractured zone height to mining height is 10.48. Affected zone range of front abutment pressure, peak of front abutment pressure and plastic zone range increase with increase of coal face advancing distance. The front abutment pressure is stable after the first weighting at basic roof, which manifests in the maximum stress concentration factor and plastic zone range basically remain unchanged. The research results can provide basis for surrounding rock stability control of fully-mechanized coal face under the similar geological condition.