Through monthly monitoring the five sampling sites in Qiandao Lake during 2007-2011, the yearly change patterns of transparency, chlorophyll a (Chl.〖WTBX〗a〖WTBZ〗), permanganate index (CODMn), total nitrogen (TN) and total phosphorus (TP) were investigated, and the spatial and temporal variations of water quality were assessed by two trophic state indices such as TLI and TSIM. The results showed that the 5 year average values of transparency, Chl.〖WTBX〗a〖WTBZ〗, CODMn, TN, and TP were (5.599±0.942) m, (2.720±1.380) ug/L, (0.857±0.168) mg/L, (0.990±0.090 2) mg/L, and (0.015 1±0.001 83）mg/L, respectively. The two trophic indices gradually decreased from the upper reaches to the lower reaches, fluctuated seasonally with the maximum in summer and the minimum in winter, and increased slowly year by year with a 5 year mean value of 26.6 for TLI and 35.5 for TSIM. It was suggested that the 5 study years was in the transitional period of trophic level from oligo to meso trophic status for this lake.