According to the contradiction of robust and realtime of image thresholding in the engineering application, a novel thresholding algorithm is proposed in this paper. Making thresholding effective based on the spectral graph theory, series improvements were taken, as weight criterion equivalent simplification, gray statistics, validity screening and gray-level division. It's occupies smaller storage space and requires much lower computational costs, using validity gray-level as segment unit. Therefore, the thresholding algorithm meets the demands on the real-time of engineering application. The examples are presented to show the superior performance of the proposed thresholding algorithm compared with other thresholding algorithm.