Abstract: In order to upgrade the design means, improve the design quality, and realize the digital delivery of railway projects, this paper took the design of railway tunnel ancillary facilities as the starting point, and proposed a design method of railway tunnel ancillary chambers based on Building Information Modeling(BIM) by combing the design process and studying optimization technology. With the secondary development of BIM software, this design method can effectively get through the upstream and downstream data of tunnel design and significantly improve the intelligent level of tunnel design. Practice has proved that the ancillary chamber design based on this method under Bentley platform can meet the needs of project BIM delivery and 2D drawing delivery under existing design specifications, greatly improve the efficiency and quality of ancillary chamber design, achieve the integration of BIM technology and traditional design, and help the railway industry to transform from BIM aided design to BIM positive design.