A freezing event in Hunan Province in February 2005 is analyzed. It is a light freezing, but it caused heavy hazard. The main reasons of the phenomena are as follows. The height of the bottom of the inversion layer is relatively low, the temperature at the top of the layer is relatively high and the wet weather remains long time. This situation led the air between 1000hPa and 925hPa to supercooled layer, which corresponds to the strong freezing region, while the cold air on the ground is a little weak. for the reasons, the surface freezing is not obvious.