Based on the meteorological data from 68 national meteorological stations in the northeastern Tibetan Plateau,China, the monthly, seasonal and annual data about the frequency and intensity of cold air and strong cooling during the time period from 1961 to 2015 are summarized and the corresponding change characteristics and causes are analyzed with climatic diagnostic method. The results indicate that,on a yearly scale, the average frequency of cold air in the northeastern Tibetan Plateau in the time period was 49.6 times,and the climate change trend rate of cold air was decreased by 0.600 times per 10 years,while the decreasing tendency was not significant. Besides, annual mean strength of cold air in the whole region was 0.39, the climate change trend rate was decreased by 0.022 per 10 years,which had significant decrease tendency, the comprehensive average strength of the cold air in the whole region was 0.67,and climate change trend rate was decreased by 0.005 per 10 years,which did not show a significant reducing tendency. On a seasonal scale, the cold air frequency had significant reducing tendency in summer,while it had a non-significant reducing tendency in spring,a non-significant increase tendency autumn and winter. In addition,cold air strength had a significant weakening tendency in winter while the tendency was not obvious in other seasons. The comprehensive intensity of the strong cooling displayed a strengthening trend in spring and weakening trend in other seasons but none of them was significant. The decrease of the polar vortex area index and other factors in Europe region of Atlantic Ocean and the increase of the sea temperature index and other factors in tropical northern Atlantic Ocean increased mainly resulted in the declining of annual frequency of cold air. However, the enhancing of B index and other factors in Tibetan Plateau and the weakening of the SST dipole index and other factors of the tropical Indian Ocean were the main causes for the weakening of cold air strength.