Abstract: n order to improve the effect of top coal caving in fully-mechanized top coal caving mining，improve the coordination mode between the subracks.optimize the coal mining process parameters and improve the coal caving rate and reduce the gangue content,the theory analysis and GDEM discrete element numerical simulation analysis method were combined to study the developmental morphology and group of fractured top coal release body - development process of initial coal release,top coal migration trajectory curve,coal sagging interface sinking dynamic curve characteristics，top coal release influence range and the coupling relationship between time and space.In this paper,the simultaneous coal injection of different combinations of the adjacent supports in the direction of the working face is referred as group coal caving.The results show that the development of top coal release is a nearly circular development process from the coal release to the coal gangue interface.and the top coal release also shows an approximate annular loose release; the development volume of the top coal outlet increases with the increase of the size of the coal discharge outlet,and it experiences three transitional stages of “vertical elliptic - quasi-circular - transverse elliptic”,in which the development width of the outlet meets the cubic function relation with the number of the simultaneous coal-supporting stents.Top coal release is a process of moving out along the path of minimum resistance in an approximate straight line,and the top coal model particles near the vertical line of the center of the coal release have priority to reach the coal release,and the migration path is symmetrical with the vertical line of the center of the coal release; the influence range and displacement of top coal release increases with the increase of coal inlet size.The displacement and velocity at the lowest point of the subsidence dynamic curve of coal gangue interface are positively correlated with the time of coal caving，there is a negative correlation between the time needed for the subsidence dynamic curve to reach stability and the number of simultaneous coal drawing racks，the coal gangue interface curve is approximately the normal distribution curve of horizontal inversion,and it is symmetrical about the vertical line of the center of coal hole.Research has certnin reference significance for top coal caving mining.