Abstract: Based on the distinguishing features of water system in Guangzhou-Foshan cross-border area in Nanhai District, different water control units were divided. By investigation and analysis of water environment control projects finished in 2018 in this area, their effects was calculated. In Guangzhou-Foshan cross-border area, the largest reduction of COD and ammonia appeared in Shuikou Channel, whose proportions were 42.9% and 62.9% respectively; the largest reduction ratio of TP, 60.1% appeared in Xinan River. On the aspect of administrative areas, the largest reduction of COD and ammonia appeared in Dali Town, whose proportions were 29.8% and 35.4%; and the largest reduction ratio of TP, 62.9% appearing in Shishan Town. Response relation between water pollutant reduction and water-quality index was established, which could be used to analyse the validity of water control units. Thus, corresponding measures on water pollutant prevention can be put forward, to provide technical support for water pollution prevention and control planning or environmental projects.