Long downhill is a typical road section with a high incidence of large vehicle accidents. Most existing simulation models are suitable for macroscopic evaluation of road horizontal line safety and cannot reflect the impact of different gear shifting decisions of drivers on driving safety on long downhill roads. Therefore, it is difficult to provide targeted measures for improving driving safety on long downhill roads. Established a complete vehicle model, steering controller, and pedal controller for heavy-duty trucks; A long downhill driving control strategy based on gear acceleration, gear coasting, and gear braking was designed by combining TruckSim and Simulink software. A virtual simulation experiment was proposed to introduce the driver's manipulation behavior characteristic spectrum at the vehicle speed level; Finally, an actual long downhill road is introduced as an example to study the driving characteristics of vehicles on long downhill roads under different driving modes. The simulation results show that the designed gear shifting downhill driving control mode can reflect the impact of different gear shifting decisions of the driver on the safety of long downhill driving. It can provide a new idea for optimizing the driver's gear shifting decision, selecting road profiles and emergency lanes from the perspective of vehicle braking force and speed change.