By the methods of cluster analysis, discriminant analysis, and factor analysis, this paper studied the spatiotemporal variations of water quality of Taoranting Lake, a typical eutrophic urban landscape lake in Beijing, from March to November 2011. At temporal scale, the water quality of the Lake could be grouped into three periods which corresponded to the rainy season, normal season, and dry season in Beijing, respectively, reflecting an obvious temporal variation. At spatial scale, the water quality of the Lake at five sampling sites could be grouped into two groups, implying the different pollution degree. Water temperature, pH, transparency (SD), CODMn, total suspended solid (TSS) , and Chl-a content were the main factors affecting the temporal variation of the water quality, and the eutrophication of the water body was mainly controlled by the water temperature and Chl-a, total nitrogen, and total phosphorous contents. The effects of TSS and organic pollution should be also paid more attention.