Abstract: Lakes play an important role in watershed water cycle, and play an irreplaceable role in regional climate regulation, promoting regional economic sustainable development and maintaining ecological environment. Quantitative lake evaporation is very important for the evaluation of water resources and ecological water demand in arid areas of northwest China. At present, the existing calculation methods of lake evaporation ignore the influence of water level depth on evaporation. Therefore, water surface evaporation experiments with different water level depths were carried out in the Ningxia Water and Environment Field Scientific Observation and Research Station, and the relationship between water level depth and water surface evaporation was explored by the Pearson correlation and nonlinear regression analysis. According to the calculated water surface potential evaporation conversion coefficient, a deep evaporation calculation model suitable for water surface evaporation in the Yinchuan Plain was fitted. The Qingshui Lake was taken as an example, and a single-beam unmanned ship was used to detect the shape of lake bed, and the depth of lake water level was obtained. The calculation model of deep evaporation was compared with the Penman-Monteith(PM) formula. The results show that the difference between the two models is 0.679 mm/d. In the trend of monthly average potential evaporation curve, the calculation results of the PM formula are obviously affected by temperature, while the relative temperature change of deep evaporation calculation model has lag characteristics, which better reflects the adjustment of water level depth to temperature and makes the calculation of potential evaporation more accurate. The depth evaporation calculation model fitted in this study improves the calculation accuracy of lake surface evaporation in the Yinchuan Plain, provides a parameter test for lake ecological research in Yinchuan, and also has a basic impact on water resources utilization and ecological environment protection in this area.