In order to improve hybrid electric vehicle’s energy efficiency, this paper did a research on the regenerative braking system of HEV. In this paper we proposed a new parallel regenerative braking control strategy for HEV and analyzed its characteristics in details. Based on theoretical analysis, we developed a parallel regenerative braking controller for a certain HEV, and built hardware-in-the-loop simulation system to test the controller’s performance. We chose the UDDS driving condition for simulation, and the result shows that the regenerative braking controller we developed is effective and reliable. The controller fulfills the parallel regenerative braking control strategy and distributes the braking force accurately. The energy recovery efficiency reaches 16.7%, which significantly improves the vehicle’s energy efficiency.