On April 20,2005, a mesoscale deformation field structure in cold vertex was fou nd in the Doppler velocity picture which showed a symmetrical structure. Frontog enesis was usually caused in the deformation field which could be found timely i n radar observation with high spatialtemporal resolution. By using the realti me radar data, satellite image and conventional data. the synoptic process was a n alyzed. It indicated that the deformation field played an important role in the course of development of the cold vortex.