Based on the meteorological data collected by automatic observation system of Dehong Mangshi A Cirport and the ECMWF 0.75°×0.75°reanalysis data,the northeast downwind weather process of Dehong Mangshi airport during November 3 to 4 in 2017 is analyzed. The results show that：The downwind weather was affected by the southward cold air, the performance of the process was high wind speed,long duration and widespread delays at Dehong Mangshi Airport.The destruction of the south branch structure by the bay of Bengal high is the main reason for the weak on southwest wind in Dehong Mangshi, and the confluence of the easterly airflow outside typhoon "dawei" and the northeast airflow outside the surface cold and high pressure made the easterly wind strengthen and dominate the surface wind,t hose caused maintaining of the northeast downwind process.The downward momentum transportation was an important factor in the process.The eastern regions in Yunnan were greatly influenced in cold air southward moving, Dehong Mangshi airport is located in the west of Yunnan, cold air has slight influence on it. So forecast the downwind exceeding at Dehong Mangshi Airport in cold air southward moving,the wind of Kunming airport and east Yunnan can be used.