Abstract： A method for designing fractional order (FO) PID controller for the high-order process with inverse response was proposed in this paper.  In order to easily design the controllers, the model of high-order process was simplified using a modified particle swarm optimization (PSO) algorithm. Based on the simplified model, a fractional order PID controller was designed according to the principle of internal model control (IMC). Since the controller has only one adjustable parameter, the complexity of the controller tuning is effectively reduced. According to the maximum sensitivity index, the analytical expressions of the controller parameter tuning was deduced, and the blindness of selecting the parameters was overcome. The simulation results show that this method can enable the system to have good set-point tracking, disturbance rejection characteristics and robustness against the parameter perturbation of system.