Abstract: In this paper, the first order lag model is used as the generalized object model of main steam temperature to design the fuzzy adaptive internal model control based main steam temperature control system. The parameters of the object model are identified under different operation conditions. According to the model parameters and fuzzy adaptive rules, the controller parameters are adjusted automatically. The designed system is simulated and applied in a power plant as well. The results show that, compared with the conventional cascade PID controller and the Smith prediction control, the system has a better control quality when the system operates under load disturbances or with model parameter deviations as well as under different operation conditions.