Li Bai's "Mount Emei Moon Song" has been famous for thousands of years, but its interpretation has been controversial and controversial. Based on "Mao Shi Zhengyi" and other documents, this article proposes for the first time that the "half wheel" in the poem refers to the first quarter moon. The first quarter moon is the moonrise at noon on the seventh and eighth day of each month in the lunar calendar. The moon phase is a semicircle. The moon is at the midday at night and at midnight. When the moon sets, the poem says "Mount Emei has a half-moon in autumn", and also says "the clear stream comes out at night (in the second half of the night)" and "missing you (the moon)". It means that the half-full moon is seen in the first half of the night and disappears in the second half of the night, which is the first quarter moon. Based on Song Huanghe's "Supplementary Notes on Du Shi" and other documents, and on the basis of previous research, it was further determined that Qingxi Station was located in Jianwei County. The whole poem talks about a boat traveling through the Pingqiang River to Jiazhou. It has already fallen into the night. The first quarter moon is accompanying people along the way. It sets off from Jiazhou before dawn the next day and arrives at Qingxi. It sets off from Qingxi before dawn again. The first quarter is the moon when setting off. The moon has already set. Although I cannot see the moon, I still miss it. It can be seen from Li Bai's poem that elegance, charm, romance and realism can be integrated in poetry.