Abstract: Doppler radar VAD technique can draw the divergence of background wind field from the distribution profile of Doppler velocity with azimuth on a distance circle. But, the distribution of Doppler velocity of a distance circle is unintegral normally. In order to calculate the divergence, the data gaps on the velocity-azimuth profile have to be interpolated artificially, which cause the calculated divergence not objective. According to the simple harmonic distribution of Doppler velocity with azimuth, the symmetric method is proposed to avoid making up the data gaps artificially. In addition, the method of area modification for calculating divergence is proposed.