To improve the aerodynamic characteristics of a cabin-over-engine truck and reduce wind resistance， the contribution of different components to the drag coefficient was studied through the wind tunnel test of the truck. It was found that the air deflector， neckline plate， rearview mirror and side skirt contributed greatly to the drag coefficient. According to the aerodynamic principle， aerodynamic drag reduction optimization design is carried out for the parts which make a great contribution to the drag coefficient such as the air deflector， and the drag reduction effect is verified by experiments. The flow field in the front of the truck is improved through the modification design of the rearview mirror and air deflector， and the flow field in the rear of the truck is improved through the parameter combination design of the deflector at the rear of the cargo box. Finally， the schemes with good drag reduction effect of each component are combined. The wind tunnel test results show that the aerodynamic performance of the truck body has been significantly improved through the aerodynamic drag reduction design. Compared with the initial model， the drag reduction effect of the optimal aerodynamic performance combination scheme is about 7%.