Abstract: Due to user mobility and favorite of collective activities, the distribution of users in WLANs is seriously uneven and changeable. When a lot of users congest in a WLAN, the WLAN performance degrades and the user experience becomes worse. To address dynamical congestion in a WLAN, existing solutions are unpractical. In this paper, through introducing shadow access point (SAP) and station mapping, a solution called splitting and restructuring dynamically (SRD) is proposed, and formal analysis of station mapping and performance is conducted, and an algorithm for the optimal mapping is devised. According to the change of WLAN status, SRD can dynamically split an overcrowded WLAN to multiple sub-WLANs and restructure them into a centralized WLAN. So, the distribution of stations in all sub-WLANs can be monitored and controlled centralizedly. SRD can reduce the number of stations in each sub-WLAN, and improve user throughput and alleviate the impact of both collisions and multi-rate. The simulation results show that SRD can improve the WLAN throughput a lot. Besides, SRD requires no modifications on user devices.