Abstract: For the problem of the broken of top coal in the face of longwall top coal caving（LTCC）, this paper analyzes the influence of depth of coal seam, thickness of coal seam, joint and fracture in coal mass, stress of abutment pressure, roof movement, bearing stress of bracket and excavation unloading effect on the broken of top coal. Based on the analysis of the research status of the mechanism of top coal broken, it is proposed that the study of the top coal broken mechanism should focus on improving the joint detection technology of top coal seam, which is to realize the in situ precise joint detection of top coal and then achieve visualization of top coal. At the same time, it is necessary to have a further study on the broken effect of bracket on top coal and propose the idea of necessary conditions for the fully broken of top coal from the energy point of view, which provides the theoretical foundation for improving the top coal fragmentation degree and the coal recovery rate.