Lake Wabu, as the largest lake in the Huaihe Catchment, is located on south bank of the middle-reach Huaihe River and serves as a flood storage area in this basin. To eliminate influence of countryside domestic sewage, this paper is to evaluate the water quality based on data at three monitoring sites and four monitoring sections in the Lake Wabu, which data were obtained during a period from October in 2011 to December in 2015. The pollution factors were analyzed by utilizing methods of the single factor pollution evaluation and the Nemerow pollution index with evaluation indicators of permanganate index, total nitrogen, total phosphorus and ammonium nitrogen. The conclusions are as follows. Water in the Lake Wabu is slightly polluted with the Grade Ⅳ, and its main pollution comes from the sources of agriculture and daily life in the basin. Some inflow rivers already are of bad water quality with abundant nitrogen and phosphorus, in which Zhuangmu River is the worst. It is necessary to renovate the basin environment comprehensively and control the effect of the agricultural non-point pollution.