Abstract: Abstract: In this research, a new water surface evaporation on-line detection device of pulse type evaporator was designed. The device was mainly composed of a whole structure stabilization device, a sensor position fixing device, a sensor position adjustment device, an Arduino Uno development board, a water level sensor, an A4988 drive board, a power module, upper computer control calculation and display storage software, Internet of Things server and data transmission module. The whole structure stabilization device was composed of a device base, a supporting rod fixed base and a supporting rod. The sensor position fixing device was composed of a motor fixed rod, a guide rail fixed pole and a probe fixed rod. The sensor position adjustment device was composed of a water level sensor, a coupler, a leading screw, a screw nut, a stepping motor, and a limit switch. The water level sensor was installed on the probe fixed rod. The limit switch was installed under the pole of the guide rail. The water level sensor could provide analog level signal and input to the interface of Arduino Uno. The 42BYGH48 stepping motor was driven by a A4988 drive board, and the drive board was supplied with pulse by Arduino Uno development board. The main interface of the upper computer was designed by Xcode software. The main functions of the mobile terminal software were to display device ID, send measurement instructions to the pulse type on-line detection device for evaporator evaporation and control its detection operation. After a detection operation was completed, it could receive message from the Internet of Things server and view the measured water level in real time; The water level value and irrigation interval parameters were calculated dynamically according to the water level value and irrigation interval parameters. The measured value of each water level were stored in the Internet of Things server. The historical measurement and its corresponding measurement time and trend map were displayed on the mobile app. The data could be viewed and analyzed at any time. In order to evaluate the accuracy and stability of the device. A total of 3 tests were carried out for each water level. The infrared optical sensor detected the change of the level of the sensor probe after the probe touched the water surface, and then calculate the water surface evaporation. Based on this sensor, the online detection of water surface evaporation was realized. The performance of the device was tested by the water surface height test of tap water. The results showed that: 1) the success rate of the water level sensor returning to the initial position was 100% in the 39 tests for the 13 water level levels. During the 39 tests, the success rate of the singlechip microcomputer development board receiving the detection instruction was 100%, indicating that the device runs reliably; 2) in the 39 tests, the maximum range of the number of pulses measured by 3 times at the same level was 3, indicating that the device runs stably; 3) The maximum relative error between water level measured by the device and the artificial method was 2.04%, indicating that the device has high detection accuracy; 4) The results of field tests showed that the device had good adaptability and good performance. The minimum relative error was 0.85% and the maximum relative error was 2.68%. The device can be used as an online detection platform for evaporator evaporation.