Abstract:Taking thirty middle-income urban families in Beijing, Shanghai, Guangzhou, Lanzhou and Kunming as the research object, relationships between household scale, household structure and emission characteristics of domestic sewage were investigated. The results showed that environmental impact increased with increasing household scale. Due to scale economic effect, pollutant indicators of COD and BOD presented marginal decrease. While the results of TN,TP were mainly influenced by individual factors of family members. Taking both household scale and household structure into account, household equivalence factor method was firstly proposed for estimating pollutant emission in different household types.