The service quality of a station in IEEE 802.11 wLAN (wireless Local Area Networks) is strongly influenced by which access point it associates with. Therefore, a key challenge is how to select an appropriate access point from multiple available ones. Conventional association protocols have been proved to be not effective. In this paper a strategy for differentiated access service selection based on users' running application is presented. The goals of the proposed strategy are: to select and dynamically reselect access point based on user's actual QoS requirements on bandwidth and delay leading to differentiated service quality provision; and to redistribute network load across access points. The effectiveness of our strategy is evaluated through simulation study, confirming better performance compared with conventional ways.