The major characteristics of weather disasters in Yunnan Province is analyzed by using weather disasters data in the period of 1950-1999, weather disasters in Yunnan Province have characteristics of multi-kinds,high frequence,overlapping,wide distribution,obvious seasonality and regionalization,few disaster formation area and serious accumulated losses. The formation mechanism and occurrence background of weather disasters in Yunnan Province has also discussed. The results show that geographical environment,climate and human activities are main factors to form weather disasters in Yunnan Province. The geographical environment elements to form weather disasters in yunnan include low latitude plateau,approaching tropical oceans,complicated topographical features,cliffy mountain,few vegetation,concentrated rainfall,complicated geological structure and strong fault actions. The strong or weak monsoon activities and the difference of general atmospheric circulation in winter and summer over Yunnan are the climatic background to form weather disasters. Population increase,excessive wasteland reclamation,denudation forest,serious water and soil erosion are main human factors to intensify weather disasters occurrence frequently and loss seriousness in yunnan. At last countermeasure of weather disasters prevention and reduction were put forward.