Abstract: In order to consume more renewable energy, thermal power units have been operating under wide load condition for a long time, and the frequent load changes have caused some difficulties in superheated steam temperature control. Taking the superheated steam temperature of a 1 000 MW ultra-supercritical unit as a research object, the differences of its dynamic characteristics under different loads were analyzed. Meanwhile, an observer-based proportional-integral-derivative (OB-PID) control structure was proposed to enhance the stability of superheated steam temperature of the unit in wide load operation, which was characterized by multi-model and nonlinearity. Simulation results show that, compared with the conventional PID control, OB-PID control not only can maintain better tracking performance, but also can improve the disturbance rejection performance and robustness of the system. In addition, OB-PID control has an extremely simple structure, and the improvement based on PID framework does not add additional signal measurement points, which has a great potential application in flexibility retrofit of thermal power units.