Abstract: The main purpose of the article is to help to get a better understanding of the working process of an electric motor in a hybrid electric vehicle. Followed the summary on the benefits of developing hybrid electric vehicles and the brief introduction to three major types of hybrid electric vehicles, this article analyzed the electric drive system and the working conditions, including the condition of starting, partial loading, full loading and braking. The analysis focused on, along with the change of given voltages (from high to low) in an electric drive system, the exhaustive physics process of the electric motor switched from driving condition to regenerative braking, and the paper pointed out the key function of motor inductance played in the process.