Abstract: The dry electrostatic precipitator equipment in coal-fired power plants is used to reduce pollution from boiler exhaust gas. In order to achieve better energy-saving and emission reduction effects, a robust second-order time-delay active disturbance rejection control method is proposed for dry electrostatic precipitators. This method avoids time-consuming gain tuning, and the bandwidth parameters of the controller and observer are scaled separately based on the parameters of the second-order plus time-delay model. The resulting scaling parameters can provide a detailed evaluation of the system robustness. Compared with traditional indexes, it reveals that relative delay margin is an important robustness index for controller gain tuning. Throughout comprehensive robustness analysis, a robust gain tuning rule is recommended for controlling the outlet dust concentration of the dry electrostatic precipitator. Finally, the control simulation and experiment of the actual dry electrostatic precipitator in coal-fired power plants are carried out, verifying the effectiveness of the proposed control method.