The construct of the Three Gorges Project will have a great effect on ecology and environment of the Changjiang River. Estuary. In order to understand the present environmental state of the Estuary before the construct of the Project, five cruises in different seasons were carried out in 122°-124°E, 30°45′-32°00'N sea areas and the river sections affected by tides The surveys indicate that COD average concentration reachs a maximum of 2.73m /L in May, nd a minimum of 1.18mg/L in October. By the results of the surveys the paper discusses the characterestics of COD distribution in the Changjiang River Estuary.