In a multi-rate 802.11 WLAN (Wireless LAN) environment, the trade-off between fairness and throughput may be a problem. In this paper, they will construct a new mathematical model called Simplified Coefficient of Variation (SCV), through controlling the power of Access Points to optimize and improve the performance of network. Since this trade-off problem is NP-hard, they use genetic algorithm solution to solve their SCV model in a practical scenario. The simulation gives excellent results that indicate their model is efficient and superior to existing method. After the experiment analysis, they use to reveal the relationships of various indicators.