Abstract: Based on PCL, a formal correctness proof of WAPI key management protocol is presented. First, unicast key negotiation and multicast key announcement sub-protocols are analyzed, and their separate proofs of specific security properties of SSA and KS are detailed under unbounded number of participants and sessions. Second, according to the sequential rule and staged composition theorem, all principals do not execute both roles of ASUE and AE, and the precondition of a sub-protocol is preserved by the other one later in the chain, so, WAPI key management protocol possesses the required security properties and achieves its predefined goals.