The thoughts of ethnicity and nation of Gu Jiegang 顾颉刚 are filled with contradictions between emotion and rationality. Despite the rationality of his academic pursuit， irrational factors such as his personality， emotions， and the atmosphere of the May Fourth Movement were important influences that led him to embark on the radical path of doubting ancient history. At the critical juncture of the Chinese nation， Gu began to reflect on his discourse of ethnicity and nation， changing his skeptical and anti-traditional stance； however， occasionally he still showed a tendency toward doubting ancient history in some informal talks， which were not without pedantic bias and emotionalism. Nevertheless， on the whole， Gu’s research on the Chinese nation insists on guiding emotion with rationality， achieving a unity of emotion and rationality. His study of the Chinese nation has evolved from deconstructing the “Chinese nation out of one” to constructing the theory that “the Chinese nation is one”， reflecting a shift in his attitude toward traditional Chinese culture from skepticism and criticism to rational understanding and love， witnessing his transformation from an anti-traditional nationalist to a pro-traditional nationalist and patriot.