Load simulator is essential to test and quality the performance of various control systems. It is good time to introduce a method to design and analyze the load simulator or since many research centers and industrial companies are trying to buy or design the load simulator. The stability, accuracy and response speed of the simulator are represented by the system parameters such as the hydraulic motor characteristics, the servovalve characteristics, supply pressure, rotational inertia, rotational spring constant, sensor and controller gains. Two design examples are shown here. A load simulator for a position control system and that for a velocity control system are designed. The goodness of the proposed method is verified by the digital computer simulations.