"Nine Chapters Arithmetic" includes nine parts: square field, millet, decline, less generality, business merit, flat deficit, surplus and deficiency, equation and pythagorean, which laid the basic framework of ancient mathematics in China. Nearly a hundred general formulas and algorithms are put forward, and the calculation-centered characteristics are established. It contains 246 application questions, which embodies the style of close combination of mathematics and practice; The basic form of the application of algorithmic commands in China's ancient mathematical works is determined. It put forward four complete arithmetic rules, such as fraction, proportion and proportion distribution law, square root and open method law, residual skill, equation skill (that is, the solution of linear equations), positive and negative number addition and subtraction law, partial area and volume formula and Pythagoras formula. All of them were correct except a few mistakes, and many achievements were in the leading position in the world at that time.