A performance analytic model based on packet arrival rate is proposed for IEEE 802.11 DCF (distributed coordination function) in infrastructure-based WLAN (wireless local area network). The model does not only take into account the factors of number of terminals, traffic loads, the binary exponential back-off mechanism, but also analyzes the impact of the finite queue system at the MAC (medium access control) layer. Each terminal is modeled as an M/M/1/K queue, and the virtual time slot is introduced to discretize the state of the queue system. Based on this, a three dimensional discrete time Markov chain is used to model the system. By using the model, normalized throughput, packet delay and packet losing ratio are obtained. Simulation results show that the proposed model can validly predict the performance of the DCF under various packet arrival rates.