This paper presents an in-depth analysis of the DCF (distributed coordination function) access mode of IEEE802.11 protocol. Based on the result of this study, the authors have developed a new self-adaptive wireless LAN MAC (medium access control) algorithm with the name of NSAD (new self-adaptive DCF algorithm). Simulation results show that NSAD is superior to DCF in all characters concerned (e.g. goodput, fairness, and packet drop rate).