Abstract: In order to obtain the damage and slip mechanism of steep longwall top coal caving face floor, this paper combined elastic- plastic mechanics theory to a nalysis the mechanical critical condition of steep coal seam floor damage. The numerical simulation was applied to simulate no supporting condition and temporary sup porting with wooden bolt condition in fully- mechanized top coal caving face of steep and thick coal seam and obtained the corresponding plastic damage zone, provide d a theoretical basis for the floor management of steep coal seam working face. The results showed that the maijor reason of floor damage was the instantaneous press ure relief of floor in the process of working face advancing. Due to the big coal seam angle, the damaged floor slipped along the dip direction which destroyed the overa II stability of roof- support- floor system. Wooden bolt on the floor for temporary supporting could effectively control the damage and slip of floor.