With secondary regulation, a novel hydraulic transmission technology, the secondary regulated loading system described here is oriented to rotational speed experiment of reduction gear or material. In this paper, the hardware structure of the system is introduced with specialties of the transducers, electro-hydraulic servo valves and the computer data collector used. Then, signal-adjusting circuit between computer control system and transducers or servo valves is designed. Next, a VC+ + control program under Windows operating system is worked out. Experiments on Step, Rectangle, Ramp and Sine Responses of the speed sub-system are done under alternative oil pressure and load. Finally, some meaningful results are given by contrasting the experimental curves.