Complex number refers to the number a+bi which can be written in the following form, where A and B are real numbers and I is imaginary unit (i.e.-1 root). Cardin, an Italian scholar in Milan, was first introduced in16th century. Through the work of D'Alembert, De Moivre, Euler and Gauss, this concept was gradually accepted by mathematicians. There are many ways to express complex numbers, such as vector representation, triangle representation, exponential representation and so on. It satisfies the properties of four operations. It is the most basic object and tool in complex variable function theory, analytic number theory, Fourier analysis, fractal, fluid mechanics, relativity, quantum mechanics and other disciplines.