According to the stages of academic history, redology in the 20th century can be divided into three stages: old redology, new redology and contemporary redology. Some people disapprove of this treatment, but name the Hundred Years Dream of Red Mansions after schools, that is, research school, textual research school and criticism school. The reason is that both the "new" school and the "old" school are studying the "skills" of A Dream of Red Mansions. There is no fundamental difference, but one school thinks that it is writing about others and the other advocates writing about itself. Since The Old Dream of Red Mansions is a fictional name that doesn't exist, the corresponding title of "new" should naturally be cancelled. In fact, this is a different perspective. One focuses on the historical stage and the other focuses on the ontological nature of redology. However, the author believes that this division is also convenient in narration from the perspective of the study of redology schools. In fact, the century-old Dream of Red Mansions in the 20th century, we say, is mainly the conflict and running-in reconstruction among textual criticism, textual criticism and criticism, which roughly outlines the historical features of the Dream of Red Mansions.