In meteorological and hydrological services，the evaporation of water surface is measured by ultrasonic sensors，whose precision is only 15 mm and measurement is easily disturbed by environmental factors.In order to solve these problems，a new evaporation measurement unit based on magnetostriction technology whose precision is up to 01 mm is presented.The related schematic circuit is given.The unit is tested for 6 months in an automatic weather station.Through comparing the results of manual and automatic methods，the feasibility of the automatic evaporation measurement unit with this technology is verified.The results indicate that this unit can be used instead of ultrasonic sensors to achieve the goal of high precision and better stability in meteorological and hydrological services.