With Daihai Lake in a typical semi-arid area as an example, the Mann-Kendall test, Hurst coefficient method, and t-test based on the ordered clustering method were used to analyze the evolution trend of water level in the lake, and the Partial Mantel test was employed and a hydrological model for lake area without enough data was constructed to study the response of the lake water level to climate factors and land use change. The results show that the water level of Daihai Lake had a significant downward trend from 1959 to 2018, with abrupt changes occurring in 1982 and 2005, respectively, and the water level will continue to decrease in the future; the water level of Daihai Lake is higher in spring due to snowmelt and lower in autumn due to water consumption, and the decrease of water level in autumn is the most obvious in the four seasons; climate change and water and soil resources use are the main factors affecting the lake water level change in semi-arid area, and the water level of Daihai Lake is the most sensitive to temperature, followed by sunshine under the condition of climate change. Due to the complex mechanism of precipitation, runoff, and infiltration in the Daihai Lake Basin, the water level of Daihai Lake responds with a lag to precipitation change, and the increase of forest and grass area in the lake basin may be an important factor causing the decrease of lake water level.