Using hourly ERA5 and the real observation data, the characteristics of mesoscale vortices during the extreme rainand snowevent in North China on February13-14,2020 were analyzed, and the development mechanism of the mesoscale vortices was diagnosed by using Circulation integral equation of relative vorticity. The results show that the average vorticity vertical profile of the mesoscale vortex activity area (referred to as the "vortex zone") follows an "S"shaped distribution, with extreme positive and negative vorticity values at 800 hPa and 400 hPa. The average vorticity intensity from 900hPa to 700hPa varies in phase with the precipitation intensity in the Beijing Plain area. The peak of vortex intensity was about two hours earlier than the peak of precipitation intensity, and the correlation coefficient was 0.76, suggesting that the intensity of lower-level vorticity has indicative significance for snowfall forecasting. From the perspective of the dynamical mechanisms driving vortex development, the positive vorticity below 800hPa in the vortex zone mainly originates from horizontal wind convergence; The upwelling motion from 800hPa to 700hPa and the clockwise rotation of wind with increasing altitude contributed more to vorticity. Compared to the snowfall process without mesoscale vortex (February 14, 2019), The structure of vorticity in the vertical direction has no "S" shape, and the intensity of vorticity in the middle and lower layers was weak, and the snowfall in Beijing was significantly lower.The existence of mesoscale vortex development in the "vortex zone" has indicative significance for predicting winter snowfall levels and extremes in Beijing.