EFI engine has the characteristics of DFCO. Sliding on the uphill with gear can save fuel and ensure safe driving. In this paper, a fuel saving and safety driving guidance system applied on the commercial vehicle is proposed. The uphill and downhill road information is predicted based on GPS and GIS. The fuel-efficient and safe speed tips are provided for drivers according to the models with the vehicle's structural parameters and running status parameters. In this paper, the taxiing equations of uphill and downhill are established, the taxiing distance is calculated according to the current vehicle speed and the slope. The vehicle's geographical position is obtained by GPS. The distance between the vehicle and the ramp top is calculated. Energy conservation calculation model and safety evaluation model are established based on energy conservation law. On a road of 8 km, it was found that the braking frequency was reduced by 50%, the energy dissipated by braking was reduced by 2.15% and fuel consumption was reduced by 3.62% after using the system.