The invention provides a polar code construction method for implementing code word optimal distribution under a memory channel by utilizing Homophonic encoding. In the method, an input information sequence meets independent uniform distribution; firstly, distribution characteristics of the input information sequence are changed by the Homophonic encoding, so that the input information sequence obeys specific probability distribution under the corresponding memory channel, which can implement channel capacity; and then the sequence which obeys the specific probability distribution is used as an input sequence of polar encoding so as to carry out polar encoding and generate encoded code words. The code words obey the optimal probability distribution under the corresponding memory channel so as to achieve an effect that under the memory channel, the polar encoding method can reach channel capacity. According to the polar code construction method provided by the invention, pre-encoding is carried out by Homophonic codes to implement optimal distribution of the polar encoded output code words, an original polar encoding structure is kept, and reachability of channel capacity under the memory channel is implemented.