According to the significant lowlevel divergence characteristics in the flow field of a downburst and the identification technology of the connected area in pattern recognition, an identification algorithm of downbursts using Doppler radar data is developed. The binary processing of radial velocity is carried out by setting the threshold of speed. The 8neighborhood method is applied for searching big speed value zones, and the big positive and negative speed zones are matched by using constraints such as distance, angle, difference of positive and negative speeds, and so on. The secondary matching for the adjacent areas is conducted on big speed zones where matching failed, thus to identify the alert area of downbursts. Some real radar detection data are used to verify the algorithm. The results show that this algorithm can detect the small scale downburst with the clear lowlevel divergence characteristic, especially for the downburst with asymmetric divergence characteristics that affected by the environment wind field.