There was a big deviation between the calculated and measured value when using commercial software to calculate the fuel consumption of vehicle driving cycle. The calculation problem of software was pointed out through analyzing the function and principle of software. Then it was put forward that transient data should participate in the calculation to reduce the error. Furthermore, the fuel consumption of vehicle driving cycle was calculated and compared with the measured data based on universal characteristic data and transient data. The results show that the error between simulation and test decreases after introducing the transient data.