Based on the structural characters of roof in fully mechanized top coal caving, mechanical analysis, mechanical calculation and simulation experiment were used to explore the particularity of roof structure in fully mechanized top coal caving. The simplified model of roof structure was built in final. The results shown that, during the mining by fully mechanized top coal caving, dynamic balance arch structure was formed by the roof and surrounding rock in working face. In the same time, multi span beam structure was formed in the tendency direction. The results of this paper would provide the theory basis for exploring the strata behavior regularity in further, and promote the safety in production of coal mining enterprises.