Newton's mechanical system, which consists of three laws of mechanical motion and the law of universal gravitation, correctly reflects the objective law of macroscopic objects' low-speed motion. It sums up the laws of motion of objects and celestial bodies on the earth, which have been completely unrelated in the past, into a unified theory, realizing the first theoretical synthesis of natural science, which is a leap in human understanding of nature. Newtonian mechanics is the basis of the whole physics and astronomy, and it is also the theoretical basis of all modern engineering technologies such as machinery, civil construction, transportation and so on.