A good performance of motion capture, which belongs to body sensor network, depends on a reasonable design of MAC protocol. The purpose of this study is to design a reliable and highly extensible protocol for applying in motion capture. The proposed MAC protocol can easily be actualized by the timer in the chip. With this MAC protocol, the network would be built quickly. One or more nodes could be added easily in the net or deleted randomly from the net. In order to verify the superiority of this protocol, a series of experiments were designed. The results showed that the mean of simulation receive frames for node1-node7 from each stage were very close to the original frames. In addition, the final Pocket Loss Rates for node1-node7 were 0.081%, 0.175%, 0.143%, 0.249%, 0.248%, 0.044% and 1.897%, which could be in the error-allowed range. Thus, this protocol is stable and reliable, which can be widely used to capture human movement signal.