In WSN (wireless sensor network), the security of message transmission is needed. GTMS (group-based trust management scheme) guarantees the security of routing by node trust. However, its description of trust is too simple to represent the complexity of the entity. Hence, based on the comparison method of cloud similarity, this paper establishes a node trust, and proposes a new routing protocol CRPCTMAS (cluster reliability protocol based on cloud trust model and the ant scheme). The performance analysis show that, based the correct judgment of node trust, CRPCTMAS can find a security route not only to guarantee the high ratio of data packet emission but also to prolong the lifetime of the network.