Due to the traditional gauge measurement need human to read, and the pressure, ultrasonic, automatic water level sensor exists problems like difficult to maintain, easy to damage, need other auxiliary facilities, this paper proposes a method that capture video images containing draft using the camera, and intercept real-time water level image from the video, after gray scale conversion, median filtering, edge detection and other treatment, calculate the results of water level. The water level data is obtained by the software identification algorithm, which has the characteristics of high measurement precision, easy maintenance, simple equipment, easy to popularize and so on. This method can be applied to the measurement of the water level of reservoir, city culvert and even the gate position.