Abstract: With the Wunan River of Changzhou set as a control unit for allocation of COD capacity, a three-layer(type of pollution source–breakdown of the pollution source–pollutant discharging unit)distribution framework was constructed.  A multi-level index system was selected layer by layer and type by type, and synthetic weight of each allocation object was calculated using product of initial weight and quantized value of each index. In the end, based on the synthetic weights, water environment capacity was allocated layer by layer. Results of the allocation are that domestic pollution and pollution from fish breeding and poultry raising are the two major targets for reduction, and their COD reduction rate is set by 41.6% and 35.5%, respectively at the first layer. The pollution reduction rate should be higher for scattered fish breeding and poultry raising than for concentrated fish breeding and poultry raising. The pollution reduction rate should be higher for rural domestic sources than for urban domestic sources. No quota is set for pollution reduction for crop farming, but for industry, especially textile dyeing and finishing enterprises, which is the priority for pollution reduction at the second layer.The quotas for pollution reduction for scattered and concentrated fish breeding and poultry raising in townships and districts and for rural and urban domestic lives are set as high as at the second layer. The quotas is higher for dyeing and finishing enterprises than for textile ones at the third layer. In this allocation system, the quotas for COD reduction for all the objects are lower than 50%, indicating that the targets areshould be obtainable.

Key words: control unit, total pollution load control, capacity allocation, index system, Wunan River control unit