The invention discloses a medium-range forecast system and method for cold, rainy and snowy weather based on atmospheric variable physical decomposition. By utilizing the atmospheric space three-dimensional multivariable and time continuous grid data outputted in the past observed, the current observed and the medium-range numerical weather prediction modes, and the physical decomposition of the climate and the weather disturbance quantity, a causality between the regional sustained low temperature, rain and snow and freezing extreme weather events and the weather disturbance prior to and during the events is established in the method. According to the invention, a physical decomposition of the climate seasonal variation field and the day-to-day weather disturbance field is carried out according to the data of day-to-day three-dimensional space grid point temperature, altitude and wind and the like of the atmosphere from the troposphere to the stratosphere in the northern hemisphere for nearly 30 years, and a database for the atmospheric climate field and the weather disturbance field can be established; and a historical database of the low temperature, rain and snow and freezing weather in south China is established according to the data of day-to-day temperature and precipitation from the national meteorological station for nearly 50 years. The invention provides not only an inquiring system for historical low temperature, rain and snow and freezing weather events, but also a forecasting system for medium-range low temperature, rain and snow and freezing weather events.