Scholars' interpretations on the sentence "Quan zhe fan yu jing" in Gongyang Zhuan, can be divided into two groups: those interpreted as "oppose to constancy" and those as "return to constancy". The former explained "fan" as "oppose", and advocated that constancy can be changed or even opposed; while the latter annotated "fan" as "return", and denied that constancy can be even changed. These two perspectives were opposite to each other, and consequently, the theory of "oppose to constancy" criticized its opponent knew only constancy without knowing expediency, on the contrary, the theory of "return to constancy" regarded its objector as the initiator of trickery. This article intends to reconsiders the theory of "return to constancy", in which demonstrates that "return to constancy" was originally an important academic topic among pre-Qin Confucian scholars, and that the original meaning of the word "quan" is "measure", but not "opposition", and then concretely analyses the typical case of practicing expediency by Zhai Zhong in the text of Gongyang Zhuan, and finally infers that the theory of "return to constancy" is more reasonable than the other.