To extend the life time and reduce the outage probability of cognitive relay networks, a cognitive two-way relay networks with power-beacon (PB) assisted energy harvesting and multiple primary receivers was proposed, and the outage performance of underlay cognitive multiple relays secondary networks adopting decode-and-forward mode and opportunistic relay selection strategy was studied, wherein the transmission power of secondary users was subject to the energy harvested from PB and the interference constraint from the primary receivers. The exact outage probability of secondary networks for Rayleigh block fading channel was derived, and the results indicated that the outage probability was monotonically decreasing with the increase of PB's transmission power or primary network's interference constraint. Furthermore, the asymptotic outage probability of secondary networks with or without interference constraint was derived, and the outage saturation phenomenon, the impact of PB's location on outage probability, and the relationship between outage probability and the number of primary receivers and relays, secondary networks' end-to-end capacity and energy harvesting ratio were studied. Simulation results validated the theoretical derivation.