Calculus is the general name of differential calculus and integral calculus, which is abbreviated as calculation in English. This is because the early calculus was mainly used for calculation problems in astronomy, mechanics and geometry. Later, people also called calculus analysis, or infinitesimal analysis, especially the knowledge of using extreme processes such as infinitesimal or infinity to analyze and deal with calculation problems. The early calculus was not developed for a long time because it could not convincingly explain the concept of infinitesimal. Cauchy and later Wilstrass laid a solid theoretical foundation for calculus, which gradually evolved into a very strict mathematical discipline and was called "mathematical analysis". The basis of mathematical analysis is real number theory. The most important feature of real number system is continuity. Only with the continuity of real numbers can limit, continuity, differential and integral be discussed. It is in the process of discussing the legitimacy of various limit operations of functions that people gradually establish a strict theoretical system of mathematical analysis.