Abstract: In this paper, we research on the transmission performance and power allocation algorithm for selective relay dual-hop decode-and-forward cooperative relaying systems over Rice fading channels in wireless sensor networks (WSNs). Firstly, we derive the closed-form expressions of the outage probability and average symbol error probability, and asymptotic expressions in the high Signal-Noise-Ratio regime. For increasing the transmission performance, then we propose an optimizing power allocation algorithm between the source node and the relay node according to the asymptotic performance. 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 the power allocation algorithm is close to the transmission performance of power searching method, but our algorithm can reduce the complexity of calculation obviously.