Abstract: Survivability is an important issue in ATM. In this paper, to solve the shortcomings of current ATM capacity management for survivability, a new mechanism （named CMGCSS） is presented, which is based on survivability importance of various services, and is composed of capacity preemption during restoration and spare capacity placement in advance. CMGCSS can provide capacity for critical service restoration even when existing spare capacity is short, and when integrated with priority restoration, it can form the adequate guarantee mechanism of critical service survivability. The results of analysis and simulation show that CMGCSS can provide guarantee conditions for critical service restoration and enhance the survivability of the network.