Based on the occurrence condition of No.6-1 coal seam in Suancigou colliery,the reasonable technologic parameters for the fully-mechanized top-coal caving of the 20 m thick coal seam is studied by use of the program FLAC2D of explicit finite difference method.Some conclusions were drawn as follows:there are significant relationships between the five factors in mining technology and the devastating effect of top coal,according to the magnitude of influence degree on the stability of top coal,the position of effect point of support’s composite force ranks first,followed by support’s working resistance,face width,coal caving distance and mining height,the reasonable mining technologic parameters of coal caving are:7500 kN support’s working resistance,6.0 m face width,4.5 m mining height,0.6 m coal caving distance,and 4.2 m distance from the position of effect point of support’s composite force to the coal wall.