As gas prices rise and the green movement grows, more fluid power companies are working to develop hydraulic drive trains for large trucks to passenger cars and wind turbines. The hydraulic drive system is more effective and efficient than traditional hybrid systems because there is less energy lost between the engine and the wheels. Specially designed for stop-and-go vehicles, the system captures energy as the vehicle brakes. When the vehicle is restarted, the series hydraulic hybrid system puts the vehicle in motion. When the captured energy is depleted, then the engine kicks in. Here, the accumulator in the system is used to recover the kinetic energy without reversion of fluid flow. Variable displacement pump/motor unit is utilized for both driving and hydro-static regeneration mode. This paper gives an insight on dynamic simulation results obtained using LMS Amesim tool. The effect of various system parameters like pre-charge pressure and hydraulic pump/motor-pump maximum displacement on system output power is discussed. Varying pre-charge pressure of the accumulator shows significant improvement in the system output power. Maximizing the system output power indirectly leads to less fuel consumption and pollution reduction in hybrid vehicles. Copyright © 2011 by ASME.