Abstract: The attenuation of chemical oxygen demand(COD) in rivers during the i cebound season was examined, and how the freezing action of ice-layer worked on the attenuation of COD was presented. The reduction model of COD in rivers by precipitation, biodegradation and freezing action of ice-layer was put forward. Via living example analyses, it should be concluded that the attenuatio n of organic pollutants operated by freezing action of ice-layer on rivers durin g the icebound season couldn’t be ignored.

Key words: icebound season, river, reduction mode, chemical oxygen demand