In general, it refers to imitating the shape of a physical object or structure in a design, and its size can be divided into miniaturization, physical type, and enlargement. Some models even have identical details to the actual object, while others imitate the main features of the object. The significance of a model lies in understanding the image of an object visually. In addition to its artistic appreciation value, it also plays a significant role in education, scientific research, industrial construction, civil engineering, and military affairs. With the progress of science and technology, people view the research object as a system and conduct research from the perspective of overall behavior. Systematic research is not about listing all facts and details, but identifying factors and interrelationships that have significant impacts in order to grasp essential laws. Establish through analogies, abstractions, and other methods. This is called modeling. The model can take various forms without a unified classification principle. It can be divided into physical models, mathematical models, and structural models.

物理模型：又称实体模型，又可分为实物模型和类比模型。①物理模型：根据相似性理论制造的实物，如飞机模型、水力系统实验模型、建筑模型、船舶模型等。②类比模型：在不同的物理领域(机械、电学、热学、流体力学等)。)，每个系统的变量有时遵循相同的规律。根据这个共同的规律，可以制作出具有完全不同物理意义的比较和类推模型。例如，在一定条件下，由节流阀和气容组成的气动系统的压力响应与由电阻和电容组成的电路的输出电压特性有相似的规律，因此可以使用更容易实验的电路来模拟气动系统。

Physical model: also known as physical model, it can be divided into physical model and analog model Physical model: physical objects manufactured according to similarity theory, such as Model aircraft, hydraulic system experimental model, building model, ship model, etc Analogy model: in different physical fields (mechanics, electricity, heat, Fluid mechanics, etc.), The variables of each system sometimes follow the same pattern. Based on this common law, comparative and analogical models with completely different physical meanings can be created. For example, under certain conditions, the pressure response of a pneumatic system composed of a throttle valve and a gas capacity has a similar pattern to the output voltage characteristics of a circuit composed of resistors and capacitors. Therefore, a circuit that is easier to experiment with can be used to simulate the pneumatic system.

数学模型：一种用数学语言描述的模型。数学模型可以是一组或一组代数方程、微分方程、差分方程、积分方程或统计方程，也可以是它们的适当组合，通过这些方程定量或定性地描述系统变量之间的关系或因果关系。除了用方程描述的数学模型外，还有用代数、几何、拓扑、数理逻辑等其他数学工具描述的模型。需要指出的是，数学模型描述的是系统的行为和特征，而不是系统的实际结构。

Mathematical model: A model described in mathematical language. Mathematical models can be a group or a group of Algebraic equation, differential equations, difference equations, Integral equation or statistical equations, or an appropriate combination of them. These equations can quantitatively or qualitatively describe the relationship or causal relationship between system variables. In addition to mathematical models described by equations, there are models described by algebra, geometry, topology, Mathematical logic and other mathematical tools. It should be pointed out that the mathematical model describes the behavior and characteristics of the system, rather than the actual structure of the system.

结构模型：主要反映系统结构特征和因果关系的模型。结构模型中的一个重要模型是图形模型。此外，生物系统分析中常用的房间模型也属于结构模型。结构模型是研究复杂系统的有效手段。

Structural model: A model that primarily reflects the structural characteristics and causal relationships of a system. An important model in structural models is the graphical model. In addition, room models commonly used in Biological system analysis are also structural models. Structural models are an effective means of studying complex systems.