Abstract: In order to improve the top coal mining recovery rate of the fully-mechanized top coal caving mining face in No.1 Underground Mine of Pingshuo,based on t he ellipsoid caving theory,the possible caving ellipsoid and practical caving ellipsoid condition equations and the relationship between the condition equations and the loos ened ellipsoid were deduced. Based on the coal caving step distance,a top coal caving technology was provided with the dynamic variation of the top coal thickness. The di fferent top coal thickness of No.4106 fully-mechanized top coal caving mining face and the top coal caving recovery rate under the different caving step distance were calc ulated individually. The results showed that when the top coal thickness was less than 4 m,the best top coal caving step distance was 0. 8 m. When the top coal thickness was ranging from4 ~ 7 m,the best top coal caving step distance was 1. 6 m. When the top coal thickness was over 7m,the best caving step distance was 2. 4 m. The study achievements were promoted and applied to other coal mining faces in No. 1 Underground Mine and the top coal mining recovery rate of the fully-mechanized top coal cavi ng mining face was obviously improved.