The benchmark is an essential issue of the performance assessment problem of the control systems. In this paper，the authors extend the theories of fundamental design limitations to model predictive control（MPC）systems to establish a performance benchmark. Considering constraints on the frequency domain explicitly，an output feedback robust model predictive controller was developed for the multi-input/multi-output systems with disturbances. The feedback controller developed could be explicitly set up，without online optimization. With this controller the closed-loop systems reached the limit of control performance，so that it could be served as the benchmark controller to assess the other MPC’s using the process routine data. The performance index was established. A performance assessment procedure was proposed for evaluating the other MPC systems. Numerical example well demonstrated the proposed performance assessment procedure.