In wireless distributed sensor network, the efficiency of energy consumption is very important in developing the techniques to extend its lifetime. Due to the random failures of sensor nodes, this paper proposes a concept of the expected energy consumption to control the success rate of message transmission, decrease the energy consumption, and measure the network performance. Furthermore, based on the minimum energy reliable path and its two algorithms, restricted shortest path algorithm and "restricted" Dijksta algorithm, an algorithm is developed to compute the expected energy consumption of a sensor network. The simulation shows the effectiveness and efficiency of the proposed algorithm. Finally, the influence of reliability threshold on the expected energy consumption of a network is simulated and analyzed.