||The traditional vehicle is often in intermittent mode, most likely to produce a lot of pollution emissions and fuel consumption. Though an electric vehicle with high efficiency and low pollution characteristics, yet the range is limited and batteries are expensive. Hybrid cars can achieve the objective of environmental protection and energy saving, but they are still expensive compared to conventional vehicles. Hydraulic hybrid vehicles use engines and hydraulic motor/pump as alternate power source. The energy storage elements are high pressure hydraulic/pneumatic accumulators thanks. With the aid of hydraulic motor/pump and high pressure hydraulic/pneumatic accumulators¡¦ thanks, the brake-generated power recovery is achieved and reused in turn for acceleration. This special topic focus on the related technologies and theories.