Abstract: In order to solve the problem of gas emission from the working face caused by the gas emission from the goaf in the fully mechanized caving mining under the condition of single thick coal seam with high gas, in this paper, the formula of gas emission in fully mechanized top coal caving face, which is not mentioned in the source prediction method, is studied. It is found that the gas emission of the top coal gas is higher than that of the fully mechanized working face. Based on the theory of rock mechanics, fluid mechanics and seepage mechanics, gas migration and accumulation of top coal is studied in combination with field test, finally, it is concluded that the gas accumulation in the top coal seam of fully mechanized top coal caving face and the immediate roof is more serious, and the direction of air intake to the return air lane, the gas concentration increases gradually.