In order to ascertain the eutrophication status, evolution trend, and its main impact factors in Lake Ulansuhai, the water quality monitoring data in July between 2006 and 2017 were applied to evaluate the eutrophication status at different monitoring sites by which could represent the typical regions of the lake. The evolution process and trend characteristics of the eutrophication of lake water nutrient status were simulated and analyzed. The key influencing factors of lake eutrophication were qualitatively analyzed. The results showed that the limit probability of slight eutrophication at the northern, western and southern monitoring sites was 0.588, 0.633 and 0.329, respectively, while that in the central and eastern monitoring sites was 0.810 and 0.536, respectively. This indicated that the water eutrophication in the northern, western and southern regions of the lake would present a slight eutrophication evolution trend. Meanwhile the central and eastern regions of the lake present a moderate eutrophication evolution trend. The physical and chemical indexes of water body played a decisive role in the lake eutrophication, among which the response probability of salinity index was as high as 55%, meaning that salinity index was the most important impact factor to the lake eutrophication. pH and water depth also played a quite important role in influencing the lake eutrophication.