To solve the water resources shortage and control the serious water environment pollution in Northern China, this paper has chosen Tianjin section of Chaobaixin River (in the north of Haihe Basin) as the study object to investigate the status and variation characteristics of the water quality during 2013. Based on the monitoring data of the chemical oxygen demand (COD), ammonia nitrogen (NH_4~+N), total nitrogen (TN) and total phosphorus (TP) concentration collected at the five monitoring sections and the three main influential factors of water quality, we have made an analysis of the spatial and temporal variation features of the water quality in the aforementioned section of the dammed river. In proceeding with our study, we have divided the weather and climatic changing situation of a full year into three different seasons for analyzing the water quality, that is, the planting season, the growing season and the harvest season in correspondence with the crop growing cycle and the climatic temperature variation. The results of our investigation show that the non-point source agricultural pollution tends to be the main pollution source for the study area. In the said area, the whole annual-round variation of water quality in the different monitoring sections and seasons proves quite great and therefore significantly intense, that is to say, there exists remarkable spatial-temporal variation of water quality due to the climate change, the dam operations and the pollution sources distribution. And, statistically, the pollution load of COD and TN can be shown in a descending order, i.e. the planting season>the harvest season>the growing season. In terms of the pollution load of NH_4~+N and TP, the order should be: the planting season>the growing season>the harvest season. The spatial analysis of the water quality in different periods indicates that the pollution load of NH_4~+N, TN and TP turns to be generally heavier in the upper reaches of the river, with the pollution of COD in the middle and lower reaches being serious. Therefore, it can be concluded that it is necessary to avoid treating the monitoring data as the mere standard for the analysis of the variation characteristics of water quality. Rather, it is necessary to pay more attention to the effects of the climatic change, the pollution sources distribution and some other influential factors on the water quality of the dammed river, in addition to conducting a more strict water quality management and control for the said different sections of the river and the different periods of a year circle.