This paper introduces a Media access controller (MAC) which is specially designed for wireless body area network (WBAN) and meets the demands of reliability and synchronization. Through whitening, CRC, RS encoding and auto-retransmitting the bit error ratio of the data transmission is decreased while the data transmission reliability is improved. This paper also introduces a simple addressing method and realizes multi-channel transmitting and receiving, which is helpful to improve the efficiency and build the WBAN rapidly.