Abstract: Based on EC reanalysis data,an extreme rain and snow weather in Beijing on 13-14February,2020 was analyzed.The results show that:（1）Large scale vortex,front,etc provided good background conditions for precipitation.（2）The mesoscale vortex in the central part of Hebei province was an important cause of extreme weather.（3）Convection improved precipitation efficiency,which led to further increase of accumulated precipitation.（4）The strong easterly flow on the north side of 850 hPa shear played an important role in dynamic uplift,water vapor transport and convergence.（5）The low content of cloud ice in-8 ～-20 ℃ layer and the height of 0 ℃ layer over 700 m were the direct reasons for the delay of phase transition in Beijing plain.（6）The boundary layer backflow was the fundamental cause of the phase transition from east to west.（7）The convergence anomaly of water vapor flux directly led to rainfall extremes.