With the large growth of wireless sensor network, the current security architecture couldn't solve the problems. This paper provides a security protocol of scheduled service based on cloud computing. The system is consisted of three groups that are domain server domain register server domain and functional server domain. The system encrypts the server address by disconnected message. Then two algorithms are proposed for dynamic key change when system should recalculate the login key. At last, the performance loss is measured for above algorithms. Meanwhile, the improvement of system is discussed by experiment results.