Traditional analytical method of over and under excavation relies on such standalone software as AutoCAD and is based on data from excavation to carry out analysis manually, so the analysis process is tedious, and analysis results cannot be rapidly obtained to guide on-site construction. Aimed at the problems in the traditional method, and based on such technologies as computer network technology, computer graphics technology, and WebGL, a new method was put forward to achieve the purposes of rapidly calculating and analyzing such key data as the zones, areas, and deviations of over and under excavation, displaying analysis results with graphics, timely feeding the results back to construction sites, etc. With its feasibility and effectiveness verified by experiments, the technology can be applied to such underground engineering as underground powerhouses and tunnels to improve the quality and safety of engineering, so the technology has good popularization value.