Bi-directional DC/DC converter is the core of the hybrid electric vehicle's energy management system and plays a key role in its energy bi-directional flow control. According to the requirement of the hybrid electric vehicle to its converter, we select the bi-directional Buck/Boost converter as the main circuit topology, which reduces the weight and volume and improves the work efficiency. At the same time, we use semiconductor soft switch technology to reduce the switching loss effectively. Dynamic models of this bi-directional DC/DC converter under different operation modes are derived, controllers corresponding to different working modes are also designed, and thus both system stability and dynamic response ability are improved. The simulation and experimental results validate the correctness of theoretical analysis.