Since the LEAP wireless authentication protocol is vulnerable to dictionary attacks, the flexible authentication via secure tunneling (EAP - FAST) was introduced by Cisco Corporation in 2004, which establishes a mutually authenticated protected tunnel to protect the authentication data. This friendly and easily deployable network access solution will be widely used in WLAN. The authors research and design this protocol in public wireless local area network, and implement the function of EAP - FAST peer, authenticator and FAST server in PWLAN integrate experimentation flat.