The intensification of human activities and the development of the economy and society have led to a continuous increase in the intensity of development in Lake Dianchi. The structure and function of the Lake Dianchi ecosystem have been seriously affected. According to the degree of ecological vulnerability and the main driving factors of Lake Dianchi, the main task is to clarify the current situation and problems of Lake Dianchi ecosystem for its precise management and sustainable development. Based on the "exposure sensitivity adaptation" model (VSD model), 3 criteria, 7 elements and 24 indicators were selected to construct the vulnerability assessment index system of Lake Dianchi ecosystem in this paper. The TOPSIS method was used to compare and select the weighting schemes. The robust test analysis was used to determine the optimal weight calculation scheme. The ecological vulnerability of Lake Dianchi in the three periods of 1980-1989, 1990-2009 and 2010-2020 was analysed, and the main driving factors affecting the Lake Dianchi ecosystem were identified to provide a reference for determining the ecological protection and restoration of Lake Dianchi in the future. The results showed that: (1) From 1980 to 2020, the ecological vulnerability of Lake Dianchi showed a trend of increasing and then decreasing. The highest ecological vulnerability was from 1990 to 2009, which was 0.502, which belongs to moderate vulnerability. (2) The main factor affecting the Lake Dianchi ecosystem was the sensitivity index, followed by the exposure index. In terms of exposure index, the main driving factor affecting the ecosystem had gradually changed from single industrial pollution to combined industrial and agricultural pollution. The industrial effluent discharge from 1980 to 1989 was the main driving factor, the construction land area from 1990 to 2009 was the main stress factor, and the chemical fertiliser application amount (converted into pure) from 2010 to 2020 was the main factor affecting the ecosystem of Lake Dianchi; in terms of sensitivity, the main driving factor affecting the ecosystem had gradually changed from water quality indicators to water ecological indicators. The water restoration capacity was the main driving factor from 1980 to 1989, and the number of native fish species was the main driving factor from 1990 to 2009 and 2010 to 2020. (3) Based on the above analysis, the main countermeasures to improve the health level of Lake Dianchi ecosystem are to improve the habitat conditions in the lake area, restore the population of aquatic organisms, and build an agricultural non-point source pollution control system.