Abstract: Handoff latency arisen in access points (APs) has become essential issue in wireless local area network (WLAN). The delay caused by handoff process affects the quality of service (QoS), such as real-time applications like VoIP. In order to resolve this problem, an improved fast handoff algorithm is proposed to confirm, authorize and connect the next AP. According to the moving speed and excursion angle, a threshold value of distance and received signal strength (RSS) is determined between mobile nodes (MNs) and the connecting AP. This algorithm has been used in a signal system of subway. The test results show that the delay caused by handoff process is reduced and the probability of success handoff is increased.