Lake ecosystem services (LES) is of great importance in guaranteeing regional and global ecological security, which provides a research hotspot in ecological economics at home and abroad. However, there are only few models and methods suitable for LES evaluation quantitatively, under the circumstance of large lake areas, a variety of types, large regional differences, lack of basic data, and so on. Based on final ecosystem services and key characteristic indicators, this paper took Lake Bosten as an example, built a model named lake ecoservice production function (LEPF) to assess lake ecosystem services valuation (LESV) and identify the contributions of key characteristic indicators quantitatively. The results showed that: (1) From 1990 to 2019, the average final services of Lake Bosten reached ￥2226.84 billion yuan, with an overall trend of "rising-falling-rising", and the dominant ecosystem services included climate regulation, flood control and water storage; (2) The LEPF fitting results nicely reflected the contribution degree of the selected key characteristic indicators on the LES, from high to low, as follows: lake water level>evaporation>area>aquatic vegetation area>integrated nutritional status index; (3) The output elasticity of the water level in the five types of the key characteristic indicators was relatively high, indicating that the fluctuation of the water level was closely related to the changes in the ultimate service value of the ecosystem.