The autumn equinox is the sixteenth of the 24 solar terms and the fourth solar term in autumn. Fight for yourself; The sun reaches 180° ecliptic longitude; It is held on September 22-24 of the Gregorian calendar every year. On the day of the autumnal equinox, the sun shines almost directly on the Earth's equator, and the length of day and night is equal around the world. Autumn equinox, "fen" means "equinox" and "half", in addition to referring to the equinox of day and night, there is also a layer of meaning that the autumn is equally divided. After the autumnal equinox, the position of direct sunlight shifts southward, and the days in the northern hemisphere are shorter and the nights are longer, the temperature difference between day and night increases, and the temperature decreases day by day.

The autumn equinox used to be the traditional "moon festival", and the Mid-Autumn Festival evolved from the autumn and evening moon festival. On June 21, 2018, the State Council issued a reply on agreeing to establish the "Chinese Farmers' Harvest Festival", agreeing that from 2018 onwards, the annual autumn equinox will be established as the "Chinese Farmers' Harvest Festival".