Abstract: Based on the conventionally observational data, a freezing rain snow disaster on the last ten days of February in 2010 in Liaoning region was diagnosed by weather and climatic conditions as well as atmospheric physical variable field, including forming reasons of generation and development, main features and key reason leading to serious disaster. The results show that a small trough splitting from low vorticity at 500 hPa moves eastwards, which is the circulation background of freezing rain weather. The unending water vapor transport and low level convergence at 700 hPa are the basic conditions of precipitation generation. The strong surface cold air is atrigger mechanism of freezing rain weather. Cold ice crystal layer in the upper level, warm melt layer in the middle and low levels that temperature is above 0 ℃, cold layer near the ground from the ground to 1-2 km upper level that temperature is below 0 ℃ and the ground temperature is also below 0 ℃, these complex inversion temperature layers are  the weather conditions of freezing rain generation. Upper warm advection is one of the key conditions for retaining warm layer structure in the middle level, which is important to warm layer. If this warm layer disappears, the freezing rain process would end. The intensity of freezing rain has a close relation with water vapor saturation in the middle and low levels, surface temperature, ascending and descending movement in the middle and low levels.

Key words: Cold air, Inversion layer, Warm wet airflow