Abstract: For the characteristics that immediate roof key strata structure has larger influence on strata behaviors in fully-mechanized caving stope, the criterion of immediate roof key strata "cantilever beam" structure is established. 8202 fully-mechanized caving face with large mining height in Jinzhuang Coal Mine is taken as an example to carry out calculation analysis and on-site verification. Results show that immediate roof key strata of thick coal seam fully-mechanized caving stope can generate "cantilever beam" structure. Under the protection of immediate roof key stratum "cantilever beam" structure, the lower direct roof is compacted and lagging; with the advancing of working face, immediate roof key stratum structure transfers to hinged structure, and presents "cantilever beam" structure, hinged structure alternately.