There are many structured P2P systems that use Distributed Hash Table (DHT) to map data items onto the nodes in various ways for scalable routing and location. DHT are algorithms used in modern peer-to-peer applications, which provides a reliable, scalable and efficient way to manage peer-to-peer networks. As a fundamental problem in DHT based P2P system, the efficient location of the node that stores a desired data item, performance and consistent lookup are important to avoid performance degradation and guarantee system fairness. This paper presents a structural prevention strategy to remove inconsistent lookups on the basic that inconsistent lookup is generated by inconsistent routing tables. The algorithms keep the routing tables consistent with the state of the nodes in DHT and maintain a ring structure guaranteeing consistent lookup results in the presence of node joins and leaves. The goal is to be able to trust a lookup result to give the actual state of the DHT.