Vehicle type and driving speed are important factors affecting the vehicle noise spectrum. Therefore, according to the noise spectrum characteristics of single vehicles, the types of vehicles commonly found on Chinese urban roads are classified and the speed interval is divided. Then, by collecting the noise data of a large number of single vehicles, the noise spectrum characteristics of different types of vehicles at different speed intervals are analyzed. Combined with the vehicle noise emission calculation model, the sound pressure level of the vehicle is calculated, and the noise spectrum of the single vehicle is calculated by the sound pressure level and the noise spectral characteristics of the corresponding vehicle type and speed. The speed distribution of each type of vehicle is estimated, and the noise spectrum of small-size traffic flow consisting of the same type of vehicle driving at the same speed interval is calculated. Finally, the noise spectra of all small-size traffic flow on the road section are superimposed to calculate the road traffic noise spectrum. This calculation method is applied to the five cases, the range standard deviation of the spectral sound pressure level between the calculated result and the measured value is 2.24,3.14, and the range of Euclidean Distance between the spectral energy contribution rate is 0.1,0.16.