Abstract: Today formulas being used in batch transportation calculate volumes of mixed sections with the average velocity instead of the real velocity. It is inexact particularly when the velocity changes violently. So a method to calculate the volume of the mixed section under the condition of velocity change is provided. Considering the irregularity of the velocity change in the real operation, the method calculates the increase of the mixed volume in a short span of time firstly, and then makes a numerical integration in the span of the whole operation period. As a result the total volume of the mixed section is obtained.