If the whole mathematics is compared to a big tree, then elementary mathematics is the root of the tree, each branch of mathematics is the branch, and the main part of the trunk is calculus. Calculus is one of the greatest achievements of human wisdom. Calculus plays a very important role in the development of mathematics. It can be said that it is the greatest creation in all mathematics after Euclidean geometry. It is also a qualitative leap in the history of mathematics! Euclidean geometry and algebra in ancient and medieval times were constant mathematics, and calculus was the real variable mathematics, which was a great revolution in mathematics. Everything in the objective world, from particles to the universe, is always changing in motion (in philosophy, motion is absolute and static is relative). Therefore, after introducing the concept of variables into mathematics, it is possible to describe the movement phenomenon in mathematics. Calculus is to look at problems with a moving idea. For example, the instantaneous speed of a bullet flying out of a gun bore is the concept of differentiation, and the sum of the distances traveled by a bullet at each instant is the concept of integration. The establishment of calculus has greatly promoted the development of mathematics. In the past, many problems that elementary mathematics was helpless were often solved by calculus, which shows the extraordinary power of calculus. Calculus is not only limited to solving the problem of variable speed in mechanics, but also gallops in the garden of modern science and technology and has made countless great achievements. At the same time, calculus is also the key to get through the channels of mathematics and philosophy! Because the most important guiding ideology of calculus is to use profound philosophies such as infinitesimal, infinite approximation (including infinite subdivision and infinite summation), to replace music with straight, to seek change with constancy, and to seek limit in motion!