Abstract The measurement of power plant boiler drum water level has important significance. In this article, a new approach of estimating the position of steam-water with the image processing technology was proposed. Firstly the quality of images should be improved by using image preprocessing. Then the height of water level gauge should be determined according to the process of binary and edge extraction. This method is proved accurately in estimating drum water level through the results of experiments. And it has applications on power plant.