Abstract: Jinji Sluice Section of Jinjiang River is the source of drinking water for Quanzhou City, Fujian Province. Protecting the water quality is significantly important to the regional economic and social development. Based on officially compiled hydrological data and observed water quality data, monthly concentration curves of three typical pollutants-COD_Mn, total phosphorus (TP) and ammonia nitrogen (NH₃-N) -for years with different levels were depicted by the methods of hydrological statistics and analysis of the relationship between rainfall-runoff and area source pollution. The area source pollution load ratio and the fragile water quality period were further determined. The results showed that the area source ratio to the total pollutant load increased with increasing annual rainfall-runoff, ranging from 30% to 74% for COD_Mn, 53% to 61% for NH₃-N and from 39% to 62% for TP, when the runoff level shifted from extremely poor (P=90%) to extremely rich (P=10%). There was a minor difference in annual average concentration of the three pollutants among average (P=50%), rich (P=25%) and extremely rich (P=10%) runoff level years, while a relatively big gap occurred for concentrations between poor (P=75%) and extremely poor (P=90%) runoff level years. The average concentrations of NH₃-N and TP had a similar monthly trend, and tended to arrive at an apex in March or April. The maximum values negatively correlated with annual rainfall-runoff. Although the maximum concentration of COD_Mn always occurred in March, a small gap occurred between the apex and other monthly concentrations. According to China's Surface Water Quality Standard, with the exception of March and April, the other monthly concentrations of NH₃-N and COD_Mn could almost satisfy the second class, while those of TP could meet the third class.