Abstract: Quality control in steel modular buildings relies heavily on dimensional accuracy management. Dimensional deviations of modular units during both factory production and on-site installation directly impact structural safety， construction efficiency， and cost. This study systematically reviewed relevant standards for steel modular buildings in China and conducted a comparative analysis of dimensional tolerance provisions for modular units and installation-stage deviations in typical standards to identify key similarities and discrepancies. Based on dimensional chain theory， a 6 m × 3 m × 3 m module unit was used as a case study to verify the prescribed dimensional tolerances. The results indicate that： 1）Steel modular buildings impose significantly higher requirements on manufacturing precision than traditional steel structures. Direct application of the component dimensional tolerances from the Standard for Acceptance of Construction Quality of Steel Structures （GB 50205—2020）， even with optimized manufacturing processes， fails to meet the box-unit precision requirements of most specialized modular building standards. Therefore， dedicated manufacturing dimensional tolerances for modular building components are necessary. 2）During the on-site installation stage， despite discrepancies in tolerances for critical parameters such as inter-module connection and horizontal positioning， the limits established for overall verticality deviation remain reasonable for their applicable height ranges. Based on these findings， this study explored the underlying causes of standard inconsistencies and outlined potential pathways for integrating intelligent technologies and a hierarchical control framework for dimensional deviations into the existing framework. This research provides a theoretical reference for future standard revisions and practical engineering applications in steel modular buildings.