The power performance and the fuel economy are both the important indexes of the automobile. To designing a certain vehicle, when the total weight, distribution of the load and the tyres are specified, in traditional ways, it needs to do a lot of the dynamic calculation work and numerous experiments to get the parameters of proper engine and power train. This paper, Based on mathematical model, the simulation for automobile power performance and economy is designed. The calculation on actual vehicle is taken with this software and calculated values are in good agreement with the practical data. The analysis of influence of some chief factors on automobile power performance and fuel economy is carried out, which can provide the reference guide for automobile design.