CSCW in design maybe work in mobile ad hoc network and security of routing protocol in MANET is one key factor. The routing protocol for MANET uses cryptographic technology to heighten its security, which makes it possible to use formal method. Considered the property of routing protocol for MANET, the drawback of BAN logic is analyzed and the security is described based on improved BAN logic. The formalization of the protocol is described and the method is presented. Taken example of SADSR, the security of routing protocol is analyzed by using the method, which proves the method is valid. A method to attack SADSR is found