Based on monitoring datum of water quality of Cao'E mainstream from 2003 to 2006,organic pollution in waterbody was synthetically evaluated,and spatial and temporal variation was analyzed.In this monitoring stage organic pollution tended to decline,but it remained medium polluting still.The result of the correlation analysis between organic pollution synthetical evaluation indexes of each section and the evaluation on biodegradability indicated that improving water quality of upper reach directely influenced improving that of lower Cao'E river.The organic pollution of Qingfeng bridge(upper 2#)section was the most serious,and the pollution degree of whole Cao'E mainstream was strongest in January.Emission of pollutant,condition of hydrology and weather of its valley were the main factors of spatial and temporal variation.The section beside 104 national highway(lower 6#) seriously influenced by industrial wastewater,and its capacity of waterboby biodegradation was lower.