The IEEE 802.11 is used to support asynchronous and time bounded delivery of radio data packets.The primary MAC technique of 802.11 is called distributed coordination Function(DCF),which is based on Carrier Sense Multiple Access with Collision Avoidance(CSMA/CA) mechanism with binary slotted exponential backoff.The basic access and the RTS/CTS access mechanisms are the packet transmission schemes employed by DCF.There have been few models to analysis the combination of the basic and RTS/CTS scheme until now.In this paper,we propose an analytical model to evaluate the throughput and delay performance of a combination mechanism,in the assumption that the distribution function of the packet length is a general function f(x).The accuracy of our model is validated by elaborate simulations.