To improve the performance of hydraulic hybrid vehicles, a power-split hydraulic hybrid vehicle is researched. The speed ratio characteristics and power characteristics of hydraulic hybrid transmission schemes of input split and torque split for a vehicle were contrasted. A new input-split transmission scheme is proposed, which is suitable for hydraulic hybrid vehicles. The parameters of key components such as pump/motor and accumulator for the scheme were matched. The vehicle dynamic model was built. The effects of parameters such as hydraulic pump/motor displacement, accumulator pressure and volume on vehicle performance under regenerative braking and accumulator auxiliary drive were analyzed. The main parameters of the hydraulic pump/motor and accumulator are confirmed, and the theoretical basis and reference for the design of the hydraulic hybrid vehicle system and the reasonable matching parameters are proposed.