Abstract: To address the issues of complex cross-sectional structures of railway stations, onerous earthwork calculation tasks, and low efficiency of traditional manual operations as well as existing auxiliary programs, this paper designed an intelligent railway yard subgrade earthwork calculation program based on an automatic contour line extraction algorithm. By parsing cross-sectional primitives into point-line structures and reconstructing them into undirected connected graphs, and integrating graphic preprocessing and fault-tolerant mechanisms, the paper achieved the intelligent extraction of outer contours, inner contours, and merged contours of multiple regions. Based on the .NET platform, the paper carried out secondary development on AutoCAD, implemented functions including automatic classification of filling areas, intelligent generation of inner and outer contour lines, automatic area labeling and statistics, as well as automatic output of earthwork tables. Application results indicate that the program can significantly improve the efficiency of earthwork calculation work: the efficiency is increased by more than twice in small-scale stations, and the efficiency improvement is more remarkable in large marshalling yards. Furthermore, the program has potential for promotion and application in fields such as demolition and land use area statistics.