The hydraulic retarder, an important auxiliary brake, has been widely used in heavy vehicles. Under the non-braking working condition, the air resistance torque in the working chamber, which is formed by the rotor of hydraulic retarder's stirring the air, causes pumping loss. This research designs a new type of hydraulic retarder, whose helium is charged into working chamber through closed loop gas system under non-braking working condition, can reduce the parasitic power loss of transmission system. First, under non-braking working condition, the resistance characteristics are analyzed on the base of hydraulic retarder pumping model; then, considering some parameters, such as the volume of chambers and the initial gas pressure, the working chamber gas charge model is established, and the transient gas charge characteristics are also analyzed under non-braking working condition. Finally, the helium circulation model is established, and the impact of the circulation system parameters on the retarder's oil filling time is analyzed. The results show that the retarder's helium charge system can reduce the pumping loss by more than 70% comparing with traditional hydraulic retarder, while the circulation system can achieve a 3% working chamber oil charge time reduction and raise the response rate of retarder.