Yuan yin (元因) used to be a common Chinese word, but it was replaced by yuan yin (原因), but we still don’t know the exact evolution of the word. This paper concludes that yuan yin (元因) was first used in the Tang Dynasty and was widely used in the Song and Yuan Dynasties. The word yuan yin (原因) was first used in the late Song and early Yuan dynasties, and gradually replaced yuan yin (元因) in the Ming dynasty, and then completely replaced it in the Qing dynasty. The original, fundamental meaning of yuan (原) is more intuitive and clearer than that of yuan (元), which is the root cause of the replacement of yuan yin (元因), and the most popular theory of “avoiding the fear of the Yuan Dynasty” is wrong. Yan yin (言因) is yuan yin (元因) of the loanwords, regional strong, only circulated in the southern region, especially common in Fujian, we can rely on the use of Yan yin (言因) to partially help determine the place of publication of the work.