Abstract: In this paper, the vehicle energy flow test of a heavy hybrid commercial vehicle is carried out on the chassis dynamometer with an ambient chamber under the C-WTVC test cycle. Energy flow characteristics, driving modes, the power system and key component working status and efficiency of the vehicle are studied. The test results show that the energy used to drive the vehicle accounts for 30.99% of the total energy. Heat transfer loss of the radiator and the motor cooling loop accounts for 8.89% and 2.6% of the total energy respectively. The remainder loss accounts for 50.67% of the total energy which includes engine pump gas loss, friction loss, combustion loss and exhaust enthalpy increase. In the driving mode, pure electric drive, parallel drive, drive power generation and the energy recovery mode account for 9.1%, 29.56%, 18.51% and 23.61% of the total cycle time respectively. The recovery efficiency of braking energy is 81.95%. There are about 65% of the engine working points located below 200 g/(kW·h) areas, and the thermal efficiency of the engine is 36.81% during the whole test cycle. About 24% of the motor working points are located in areas with a mechanical efficiency exceeding 94%. About 53% of the motor working points are located in areas with a mechanical efficiency below 92%, which mainly appear when the motor is driven by the engine to generate electricity or recover energy. This study provides guidance for improving the energy efficiency of hybrid commercial electric vehicles, and the following research can be focused on reduction of engine remainder loss and optimization of engines and motor working points.