Abstract: In this paper, we propose a cooperative relay transmission scheme based on energy efficiency in clustered wireless sensor networks. In our scheme, the source cluster head selects the optimal neighboring cluster head as the relay node with the channel state information between the source cluster head and neighboring cluster heads. At the destination, a distributed reception protocol is devised based upon a Maximal Ratio Combining algorithm. To decrease energy consumption, the relay adjusts the transmission power depending on receiver feedback that the adjustment information is defined in the ACK frame according to receiving Signal-Noise-Ratio threshold. Then we derive the closed-form expression for the average symbol error probability based on partial channel state information. At last the Monte Carlo simulations are given to validate our analysis. The results show that the theoretical value is identical to the simulation value and our scheme can improve energy efficiency evidently without additional energy consumption.