Abstract: The E₆₀₁ type of water surface evaporator which is populally using in china has more obvious observation error and is considerabely obstructed by environmented factors because Tron brace of observation needle causes greater evaporation then used, the change in water level in the evaporator gets evaporation unstable and overflowing system unperfect. According to evaporation, author demounted the observation, needle and Trace, improving overflowing system. In 1983, the E_{601 K} type of water surface evaporator was tested and developed. After many years of application, some experimental results were obtained, The measured value is 10.9% smaller than improved E₆₀₁ type, E_601k evaporator was buried near a lake bank, which can correctly provide evaporation value of lake face.