Abstract: In the speed control of boiler induced draft fans in thermal power plants, constant differential technology is mainly used to design speed controllers, which are easily affected by fluctuations in swing errors, resulting in excessive fluctuation range of control speed. Therefore, a variable domain fuzzy PID based speed control method for boiler induced draft fans in thermal power plants is proposed. By combining the cross-sectional state of the induced draft fan blades, a speed control balance model for the boiler induced draft fan in a thermal power plant is constructed. The operating position vector is determined, and a second-order differential equation is used for centralized processing. A variable pitch actuator is added to adjust the fan speed angle and calculate the dynamic parameters of the induced draft fan blades; consider time-domain state calculation of partial differential equation factors, complete subsystem state and control input-output transition, and divide typical tremor zones; using variable domain fuzzy PID to design a boiler induced draft fan speed controller, setting the original input variables, considering the speed oscillation relationship to switch control signals, introducing a scaling factor for expansion adjustment, setting the input quantity and control language, thus completing the speed control of the boiler induced draft fan in thermal power plants. The experimental results show that the proposed method has a small fluctuation range in the speed control of the induced draft fan at different times, meet the precision requirements of medium frequency conversion speed control, and does not have the problem of unstable furnace negative pressure.