A hydraulic hybrid powertrain for passenger vehicle is studied in this paper. The hydraulic hybrid powertrain consists of a hydro-mechanical transmission and a hydraulic accumulator. The key component of this hydro-mechanical transmission is a pressure-controlled hydraulic transmission. It combines pumping and motoring function in one unit and is potentially more competitive in terms of both energy efficiency and cost effectiveness than a conventional hydrostatic transmission. By feeding the output flow of the pressure-controlled hydraulic transmission to a variable displacement motor coupled to the transmission output shaft, a more compact and simpler hydro-mechanical transmission is constituted. In this paper the systematic approach of applying the hydraulic hybrid powertrain to a passenger vehicle is studied. A dynamic simulation model is developed in Simulink and the U.S. EPA’s urban cycle is used as the test driving cycle. A rule-based energy management strategy (EMS) for the hydraulic hybrid powertrain has also been developed. The system parameter design, controller design and the energy management strategy are evaluated through simulation.