In the structured peertopeer network,the churn caused by nodes’ joining and leaving frequently increases the cost of updating the routing table. With the problem of churn,which is difficult to handle by DHT,the concept of inverseneighbor nodes is proposed. This  means the node is in their routing tables. The number of inverseneighbor nodes for six DHT networks is computed. We find that the most significant factors affecting churn are routing, neighboring nodes selection, bootstrapping and the recovery policy,and the parallel lookup. In any two existing DHTs, there are at least two different policies in the five policies . Therefore, the method that compares the routing tables update costs of two structured p2p network directly cannot decide which policy can deal with churn better, so we propose a new method of analysis: CSP. By improving the existing DHTs,we compare each different policies by CSP. The experimental results suggest that iterative routing, fast bootstrapping, periodic recovery,and the effective neighboring nodes selection algorithm can decrease the cost of updating the routing tables in high churn.