By analysis on the principle and structure of the parallel hydraulic hybrid excavator, an improved hydraulic hybrid scheme was proposed which uses a two-way hydraulic motor to replace the hydraulic secondary regulation pump and controls the assistant power loop by switching valve in different states. After modeling the new system with Simulink software, the parameters of the components and control method were determined. The double speed points control strategy was test on the improved parallel hydraulic hybrid excavator. The engine speed and the output torque of the assistant hydraulic power system were adjusted by an engine speed PID control method integrated with the load forecasting. The simulation and experiment results showed that the control method could effectively improve the engine speed fluctuation in the hydraulic hybrid system, and make the speed stable near the target speed, so energy-saving increases by 14%.