We propose rate adaptation in the entire downlink process of transmission in channel-network combining coding systems. In current literatures, rate adaptation is discussed in channel coding or network coding separately and in traditional channel-network combining coding cases, network coding rates are generally 1. This paper is based on a one-source multi-destination wireless downlink communication system and a novel scheme of rate adaptation is applied. Our scheme of adaptation works between channel coding rate and network coding rate and its influence on system performance, which is given in form of simulation in the last chapter of this paper, shows that it works well for deducing system BER.