Abstract: The real-time monitor flow diffusion process under surface irrigation is the key content of field evaluation of surface irrigation system. The real-time measurement data supply fundamental basis for numerical simulation and system capability evaluation. A water depth measuring device applied under surface irrigation condition was developed and measured. It can automatically measure and record the variation of water depth at given points, as well as the advance time and recession time. The device has been examined under the indoor and the field conditions. The application results show that the adopted sensor is sensitive to the dynamic variation of the water depth with measuring precision ±5 mm. However, the depression of the device caused by the irrigation could produce (8±3) mm errors for water depth measuring when the field is irrigated firstly. The effect of the depression could be omitted for succeeding irrigation. The device shows high precision for measuring advance time with the relative error is less than 11% while the maximum relative error for recession time is 29%, indicating the limitation to use the device for measurement of recession time. The device could be basically satisfactory for the dynamical measurement of water depth for surface irrigation.