Lake ecosystem in Tai Lake (CH: Taihu) provide people with both direct and indirect benefits which are called ecosystem services. However, lake ecosystem services in Tai Lake have not well recognized and accurately quantified in past years. Decades of wastewater discharge, industrial pollution, and over application of chemical fertilizers around the basin have transformed this once meso-oligotrophic lake in the 1950s into its present hypertrophic state. As a result, cyanobacteria blooms appear during every summer in recent years, which may in turn have serious impacts on lake ecosystem functions and services delivery. In the late May of 2007, heavy cyanobacterial blooms dominated by Microcystis and their harmful metabolites occurred in the water columns of the northern region of Tai Lake resulting in a world-shaking drinking water crisis in Wuxi, Jiangshu Province, China. The best way to understand the deterioration of ecosystem service functions of a lake is to assess its ecosystem service values. Tai Lake, as a typical lake in eutrophication in China, was selected as a case study and data of ecosystems of Tai Lake were collected over the last 10 years. An integrated method of economy and ecology was applied to estimate the value of lake ecosystem service functions. Ecosystem service functions of Tai Lake were divided into four main categories including provisioning, regulating, cultural and supporting services. The four categories were subdivided into eleven subcategories which covered water supply, aquatic products, shipping, climate regulation, soil and sand transportation, water purification, flood control, water resource storage, soil conservancy, maintaining biodiversity and tourism. Total values of ecosystem services for Tai Lake in 2000, 2003, 2007 and 2009 were 1628.0 × 10⁸, 1908.7 × 10⁸, 1504.0 × 10⁸ and 3528.7 × 10⁸ Yuan RMB, respectively. An increasing tendency of total value of ecosystem service of Tai Lake was observed in each year except 2007. The main ecosystem service functions changed from supply function to culture function from 2000 to 2009. The main function of Tai Lake was water supply in 2000, the value of which accounted for 43% of the total ecosystem service value. However, the main function of Tai Lake changed to transportation function whose values accounted for 41.31% and 38.73% of the total value in 2003 and 2007, respectively. The main function changed to tourism function in 2009, the value of which accounted for 52.52% of the total value. The value of transportation and tourism service of Tai Lake underwent a sharp increase in recent year while the value of water supply went through a rapid decline resulting from too much attention paid to the development of transportation and tourism industry, which is not good for the continual, healthy and stable development of Tai Lake in the long run. Cyanobacteria blooms had an adverse effect on the value of ecosystem service of the Tai Lake by decreasing values of supply, supporting and cultural functions. Our research suggested that Tai Lake ecosystem play an important role in supporting and protecting human well-being. Valuation of changes of ecosystem services of Tai Lake provided the decision makers information of benefit of lake protection and effective management of lake ecosystem.