In this paper, we focus on studying the optimal joint relay positioning and power allocation for two serial relays' transmission. We consider that information exchanges in Rayleigh flat-fading channels between two end-users which have symmetric traffic requirements in terms of the data rate. Multiple serial half-duplex relay nodes are employed to extend the communication coverage and assist the bidirectional communication between two end-users using the analog network coding protocol. With the objective of minimizing the total transmitting energy at the required data rate c, we investigate the optimal relay positioning and power allocation and then propose sub-optimal solutions for a two-serial-relay one-way channel and a two-serial-relay two-way channel due to no close-form optimal solution. Simulation results demonstrate a consistency with our proposed schemes.