In order to eliminate the disturbance of speed and external load in pump controlled motor system, a constant speed control system which composes of variable displacement pump and fixed displacement motor as a research objective is established. The control principle of pump controlled motor system was expatiated, and then mathematical models of the hydraulic pressure system were derived. A kind of compound control was adopted for the system which based on optimized incremental proportion integral derivative (PID) and feedforward control technology. Simulation models were established for the system's responding situation with Matlab/Simulink software. According to the result, it is shown that control system has a swift response under the two disturbances which are the motor output speed keeps stable as required. The laboratory table is built, with the loadbox was used to simulate the change of load and using transducer to simulate the change of speed. When the input speed is kept at 800 r/min and 1 500 r/min, the motor speed returns to the setting value in two seconds, the stable state fluctuation ratio is 0.5% and transient adjustment ratio is 5.33%, while speed and load changed suddenly. Analysis experimental results show that speed control system can satisfy the design index with better regulation ability, and also provide the effective reference significant for the achievement of vehiclebased electric generator system.