Abstract: A large number of lakes exist in the Ordos Plateau. Lake evaporation, as the main discharge of surface water, is one of the key equilibrium terms for accurate evaluation of water resources. Research on lake evaporation is of important practical significance and scientific value for understanding regional water circulation, evaluating water resources and ecological environmental protection of lakes. However, the actual data of lake evaporation in this area are limited, and most of them are calculated by the conversion method and formula method. In this work, an in-situ test was carried out near the Mukainao lake, a typical lake in the Ordos Plateau, to measure water surface evaporation with an evaporator placed in the center of the lake. In this paper the correlation between evaporation and meteorological factors is analyzed. The evaporation of the lake water in situ is compared with the evaporation in the small evaporator on the lakeside and the theoretical value by using the Penman Equation. The results indicate that evaporation of lake water is more affected by humidity and temperature. The conversion coefficient of lake evaporation and small evaporator on land surface is about 0.85, which is higher than that in the previous studies. The effect of salinity on evaporation of lake water can be negligible. Compared with the calculation result with the Penman formula, the correlation result is higher. The lake evaporation can be estimated with the Penman formula in the absence of measured data.