This paper has first presented an in-depth analysis on the DCF access mode of IEEE802.11 protocol.Based on the result of the study, a new self-adapt Wireless LAN MAC (Medium access control) algorithm (NSAD)is proposed to enhance the system performance in heavy contention condition. Numerous simulation results have shown that in heavy contention condition the new algorithm is superior to the original DCF algorithm in all the characters concerned (e.g. throughput, fairness).