However, in the novel mother saint, a special method is adopted in dealing with the plot of incest between mother and son: dual personality. The dual personality mentioned here is not a simple second personality, but there is another evil soul in the protagonist’s body, which is a bit similar to the seizing of the house in the fairy novels. The adjustment of the saint mother is completely carried out by the demon who controls the main character’s body. And the saint mother, in her own sensitive constitution and the demon’s superb double cultivation evil law, eventually degenerated into the desire of the body. In this process, as a mother, she was touched and played by her son’s hands, and was finally violated and insulted to a climax. In her strong sense of shame, she was stimulated to break through taboos. As a son, although her soul was imprisoned, all kinds of feelings were still there. In the process of abusing her mother’s parents again and again, she felt guilty and enjoyed pleasure, And with the deepening of this feeling, the idea of possession of the mother finally came into being. Thinking of this, I can’t help but applaud for the ingenious layout of the author. In this way, the moral barrier of mother and son is successfully broken through with the help of others.