Abstract: The exposed upper plate and roof area of the No.2 ore body mined-out area of a multi-metal mine in Inner Mongolia is about 0.1 million square meters，and the mined-out area is in irregular shape with wide distribution and staggered overlapping.According to the status of mined-out and the existing production facilities，the method of compulsory caving rock on the plate and inducing rock avalanche on the disk gradually filling mined-out area is recommended through comparative analysis，forming the buffer security cushion with a certain thickness above the operation area.Also，how to determine the safe thickness of the buffer cushion is researched，thus providing a reference for the similar large mined-out area.

Key words: Multi-metal mine, Treatment of mined-out area, Caving wall-rock, Buffer cushion