As the existing models analyzing the back-off scheme in 802. 11 DCF can not effectively consider the neighbor nodes, this paper proposes a new approach to the performance analysis of unsaturated 802.11 DCF protocol, deduces the formulae of the MAC （Medium Access Control） layer delay and its delay in unsaturated single-hop 802.11 DCF network, and analyzes the effects of packet arrival rate, node number and collision window size on the MAC-layer transmission collision probability, the delay and the delay jitter. Simulated results indicate that the transmission collision probability, the delay and the delay jitter all increase with the packet arrival rate and the node number, and that the delay and the delay jitter both decrease with the minimum collision window size of DCF, following by an increase in the transmission collision probability.