The Zhou Bi Suan Jing (周髀算经), The Arithmetical Classic of the Gnomon and the Circular Paths of Heaven, is one of the oldest and most famous Chinese mathematical texts composed in Western Han Dynasty.

This book dates from the period of the Zhou Dynasty (1046 BCE—256 BCE), yet its compilation and addition of materials continued into the Han Dynasty (202 BCE – 220 CE). It is an anonymous collection of 246 problems encountered by the Duke of Zhou and his astrologer Shang Gao. Each question has stated their numerical answer and corresponding arithmetic algorithm. This book contains one of the first recorded proofs of the Pythagorean Theorem.

The book demonstrated the Theory of Canopy-Heavens in astronomy, making it systemized and mathematical. Giving illustrations on the Sifen (quarter remainder) calendar, it also applied complex fraction operations, extraction of square root and linear interpolation in mathematics, while raising the issues of arithmetic progressions and linear indeterminate equation. It is the earliest work that quotes the Pythagorean theorem among all documents in China.