The field theory based on the principle of quantum mechanics is the basic physical theory of microscopic phenomena. Field is the basic form of material existence. The main feature of this form is that the field is scattered in the whole space. The physical properties of the field can be described by some quantities defined in the whole space (for example, the properties of electromagnetic field can be described by electric field strength and magnetic field strength, and can also be described by three-dimensional vector potential A(X, t) and scalar potential E (X, t)). These field quantities are functions of space coordinates and time, and their changes with time describe the motion of the field. The field at different points in space can be regarded as independent dynamic variables, so the field is a system with continuous infinite degrees of freedom. Field theory is a theory about the nature, interaction and motion law of fields. Quantum field theory is a field theory established and developed on the basis of quantum physics, that is, the principle of quantum mechanics is applied to the field and the field is regarded as a mechanical system with infinite degrees of freedom to realize its quantization. Quantum field theory is the basic theory of particle physics, which is widely used in many branches of modern physics, such as statistical physics, nuclear theory and condensed matter theory.