Due to the rigorous time limit of drain tunnel in JinpingII Hydropower Project， compact plane layout that can satisfy the requirements of quick TBM assemble is designed for the TBM assemble cavern, minimal crosssection that can satisfy the assemble is designed, reinforcement pattern consisting of rock bolts, shotcreting and wire meshing is designed. The design plan of the TBM assemble cavern is favorable for the ontime boring the TBM.