Abstract: The classical French had approximated perfection in the late 17th century. On the one hand, it broke the monopoly of Latin in French culture. On the other hand, it provided a stable language foundation for French Enlightenment. In addition, French was also an important analytical method, which expanded the research scope of French Enlightenment to the field of linguistics and analyzed the main issues in a different way from traditional research, including the formation of public sphere, educational reform and national identity. Therefore, the perfection of classical French is not only a linguistic issue, but also a political-cultural issue.