Based on the survey of city bus driving condition in a typical line in Chengdu city,a hydraulic system was designed to recover the energy wasted in frequent braking. In order to research the performance of the system, a simulation was proceeded in AMESim. The result shows system with variable displacement pump/motor can achieve better performance than system with fixed displacement pump/motor; in driving cycle, this system can get an energysaving efficiency up to 38.83%.