Abstract: Aiming at the functions and requirements of the MAC protocols in Wireless Sensor Networks, this paper proposes an improved MAC protocol based on CDMA. According to the changes of network traffic, listen／sleep mechanism keeped most nodes in sleeping to save energy. And combined the technology of CDMA, the nodes used the high-speed pseudo-random code (PN) with the characteristics of uniqueness in network and orthogonality to modulate data signals, which can be overlapped in time and frequency, to achieve transmission in large-scale and real-time. Simulation results show that the protocol not only maintain lower system delay and higher through put, but also reduce energy consumption obviously.