Abstract: Reducing evaporation from lakes is important for maintaining the sustainability of lake ecosystems in arid and semi-arid regions. Quantifying the reduced evaporation of different cover measures on large lakes is a vital issue that needs to be solved urgently. In this study, we combined experimental observation data and numerical simulation techniques to modify the parameters of Penman-Monteith formula based on genetic algorithm, and then simulated the evaporation variations of different cover conditions. The reduced evaporation of Daihai Lake under different cover conditions was also estimated. The results are as follows. The corrected parameters of the P-M formula can effectively simulate the evaporation under various cover conditions with an error of-5.1%～12%. The PE ball has a better performance compared with the benzene sheet in reducing evaporation, and the 8cm black PE ball has the best performance. It is expected to reduce 0.81 billion m~3 of evaporated water loss if the 8cm black PE ball was used to cover the Daihai Lake during the period of July 2021 to October 2023. The results can provide a scientific basis for the determination of the programme to reduce the evaporation of the Daihai Sea at next stage.