In a hybrid hydraulic vehicle, the hydraulic accumulator is used as the secondary power source in addition to the engine to propel the vehicle. Since the accumulator is a passive power source, it will be only used to compensate the difference between the power demand and the power delivery by the engine. Obviously, the main energy consumption is the engine. Hence a straightforward strategy to improve the fuel economy is to reduce the engine operating period. In contrast, because of the low energy density characteristic, the accumulator can only afford the required power in a short period. As a consequence, the hydraulic hybrid vehicle has been concluded only suitable for start-stop-and-go driving pattern. This paper present different rule-based control schemes for a 3.5- ton series... hydraulic hybrid truck. The simulation results indicate that by applying suitable control scheme, the proposed series hydraulic hybrid system offers improvements of fuel economy for both urban and highway driving condition. The improvement is of 42.67% and 36.56% for urban and highway driving conditions, respectively in comparison with the corresponding conventional vehicle.