Vehicle platooning can improve traffic efficiency with access to better fuel economy and environmental benefits. The work selected the car model of DrivAer closer to the actual passenger car and used the new generation of CFD (Computational Fluid Dynamics) simulation software XFlow to simulate the energy efficiency of passenger car platoon. The vehicle fuel efficiency model based on the aerodynamic drag coefficient CD was deduced by using the vehicle driving equation. Three body types of car model, which are fast back, step back, and straight back, were selected to form a platoon separately; the number of car is two and the distance between two cars is 1 L (L is the vehicle body length) in the platoon. The fuel economy of vehicle platoon was obtained through simulation combed with the fuel efficiency model, and sorting results are fast back < step back < straight back. Besides, step back car model and 11 kinds of vehicle distance between 0 and 3 L were selected, 3 cars were made up of a platoon, and those of the platoon analyzed the relationship between vehicle distance and aerodynamic drag, the relationship between vehicle distance and fuel saving rate. The average fuel saving rate of cars in the platoon was about 4-8%, and it was dramatic decline as vehicle distance changes from 0 to 0.5 L; but when the distance is bigger than 0.5 L, it was almost not changed. Setting the distance between two vehicles to 1 L, the authors studied the fuel economy of two-vehicle platoon running at seven kinds of speed. With the increase of speed, the fuel saving rate of each car has increased and it is bigger for rear car than that of front car. The work can provide a technical basis for the control strategy of vehicle platooning in intelligent and networked traffic system.