In order to overcome the difficulty of controller design and parameter tuning for complex high-order controlled object, a design method for fractional-order robust controller based on model order reduction is proposed. Firstly, the complex high-order model is approximated to a reduced-order fractional-order model with time-delay links. According to the Nyquist curve characteristics of the original model and by using the sequential quadratic programming method, the parameters of the reduced-order approximated model are obtained. Based on this, the structure of a fractional-order controller is designed, and the new numerical calculation methods of the robust index of maximum sensitivity and the controller parameters to be tuned are deduced. Finally, the controller parameters are tuned based on the performance index in composite time domain. Simulation results show that the proposed parameter solving method for model order reduction does not need global optimization, has a fast convergence speed, and the reduced-order model approximates the original system very well. The designed robust controller enables the original system to have a good control quality.