Abstract: The paper analyzed principle of traditional roaming handoff of WiFi network, pointed out that authentication process is a main factor of long handoff time, and proposed a roaming handoff scheme of threshold handoff strategy and pre-authentication mechanism, namely pre-authentication is made before workstation does handoff, and gained AP information is stored in cache; connection status of AP is monitored in real time in course of normal communication of workstation; workstation will make judgment according to the threshold handoff strategy to ensure necessity and reliability of the handoff. The strategy and mechanism can shorten handoff time effectively, realize seamless access of workstation in APs, which provides technical support for promotion and application of WiFi.