Abstract: To address the complex control process of a variable air volume (VAV) air conditioning system, a mathematical model of an air-conditioned room under VAV air conditioning mode was established. The variable universe parameter self-adjusting Fuzzy PID control method was applied to room temperature control. The control system was simulated using the simulation module of MATLAB software. Results show that the variable universe parameter self-adjusting Fuzzy PID control method has fast dynamic response, small overshoot, and strong robustness, providing guidance for both theoretical research and engineering practice. Keywords: Variable air volume; Changeable discourse; Self-adjusting; Fuzzy control; Simulation Abstract: Based on the complex control process in VAV system, the mathematical model of the room in the way of VAV is obtained, and the changeable discourse Fuzzy PID control method is applied to control the indoor temperature. The control system is simulated by using the software of MatLab. The result shows that the changeable discourse Fuzzy PID control method has fast response, small overshoot, and strong robustness. This paper has practical guiding effect in the theoretical research and engineering practice. Keywords: Variable air volume; Changeable discourse; Self-adjusting; fuzzy control; Simulation 0 Introduction Variable air volume (VAV) air conditioning system adapts to room load changes by changing the air supply volume of each room, so that the air volume delivered by the system is transferred between each room, thereby reducing the total design air volume of the system [1]. However, due to the complexity of its control process, it generally includes multiple loops such as room temperature control, air handling unit control (linkage control of fresh air, return air and exhaust air, minimum fresh air volume control and preheating control, etc.), system static pressure control and indoor positive pressure control, and there is coupling between each loop, making it difficult to achieve good air conditioning effect, which restricts the promotion and application of variable air volume systems in China. This paper takes room temperature as an example to explore the application of variable domain parameter self-adjustment control method in room temperature control of variable air volume system. 1 Mathematical model of control system Mathematical model is a mathematical description of the behavior law of things, which describes the behavior law of things under steady state. The mathematical model of the controlled process is a mathematical description of the relationship between the output and input of the controlled process [2]. The mathematical model of the control system mainly includes the control law of the controller, the characteristics of the actuator, the mathematical model of the controlled object, the characteristics of the measuring transmitter, etc. For details, please click: Simulation of room temperature self-adjustment control system of variable air volume system