Abstract: The orientation of the Nine-Post Foundation in the sacrificial zone of the Jinsha Site in Chengdu exhibits astronomical attributes: its southeastern orientation aligns with the local sunrise direction on the Winter Solstice; the orientation from the Nine-Post Foundation towards the Soil Platform of Yangzishan corresponds with the sunrise directions on the days of the Start of Summer and the Start of Autumn. Archaeological and astronomical analysis indicates that by the late Shang to early Zhou period (around 3,000 years ago), the inhabitants of Jinsha already had the ability to determine key solar terms in the Sun’s apparent annual motion, including the Spring Equinox, Summer Solstice, Autumn Equinox, Winter Solstice, as well as the Start of Spring, Start of Summer, Start of Autumn, and Start of Winter. They had established a complete calendar system with clear concepts. The Foundation serves as clear evidence of Chinese people in remote antiquity grasping the laws of the Sun’s movement and then creating a calendar.