In order to evaluate the performance of IEEE 802.11 distributed coordination function（DCF） with unsaturated traffic,the procedure of DCF backoff and the queuing buffer of media access control（MAC） layer are modeled,and a model based on closed queuing networks is established.Then,the expressions describing the transmission rate and the throughput under unsaturated traffic load are deduced by employing the proposed model,and the effects of the terminal number,the traffic load and the package size on the network performance are analyzed.Simulated results show that the proposed model can effectively evaluate the unsaturated performance of DCF.