In order to accurately quantify the impact of the reservoir on the surrounding local climate, a quantitative analysis method of reservoir impact is proposed. Taking the Xiaolangdi Water Conservancy Complex as an example, based on the measured data before the construction of the reservoir, the correlation between climatic indicators of the surrounding stations and the reference stations was established to predict simulated climatic indicators under the scenario of no reservoir in the evaluation period, which were then compared with the measured climatic indicators to quantify the impact of the reservoir on the surrounding local climate. The results show that the Xiaolangdi Water Conservancy Complex played an important role in lowering temperature and increasing relative humidity annually and interannually during 2000-2019, which lowered the annual average temperature by 0.46 ℃ and increased the annual average relative humidity by 3.78%; the climate regulation effect of the Xiaolangdi Water Conservancy Complex weakened the impact of regional aridity, compared with 1980-1999, the increase of temperature in surrounding meteorological stations was 0.33 ℃ smaller than those in the reference stations and the decrease of relative humidity was 4.29% smaller during 2000-2019. The proposed quantitative analysis method of reservoir impact eliminates the impact of regional climate change on local climate change around the reservoir, and improves the accuracy of the analysis results.