Twoway relaying (TWR) will be faced with the problem of QoS degradation because of timevarying channel when it is applied to the future applications such as aeronautical adhoc network and vehicle adhoc network. The channel model has been built which consider the correlation between two data transmission phases. The optimal power allocation (OPA) strategy to improve system performance is proposed, where minimizing the system outage probability is used as the optimization objective. The results produced by the MonteCarlo simulation show that the proposed OPA strategy can enhance the system outage performance efficiently compared with equal power allocation (EPA) strategy under different signaltonoise ratio (SNR) and different channel correlation coefficient, and more performance enhancement can be obtained with smaller channel fluctuation. Therefore the twoway relaying with OPA can be deployed in the highspeed motion environment such as aeronautical adhoc network and vehicle adhoc network.