The conventional construction of polar codes is designed in advance for a specific channel, the performance of polar codes deteriorates if the construction does not match the current channel. In other words, we suffer from performance loss when either a time-variant channel or an inaccurate estimation of channel are considered. To put polar codes into practice, a channel-aware construction of polar codes, which optimizes the construction on the fly, is proposed in this paper. Unlike universal polar codes, the receiver of the proposed scheme does not need to know any knowledge of actual channel. In addition, the proposed algorithm constructs polar codes only based on decoding results, it is well suited to not only i.i.d. channels but general channels. Simulation results show that the proposed schemes over a time-variant parallel channel (i.e. multi-channel) are always achieved a relatively good performance.