With the gradual expansion of subway networks,more and more subway lines are constructed and opened in stages due to such constraining factors as planning,approval and requirement change.How to achieve the full-functional access of the signal system without affecting the normal operation of an existing line is the key issue for the opening of the subway line.Based on the implementation experience accumulated in the signal system engineering project for the northern section of Phase Ⅱ of Dalian Metro Line 2,this paper proposes a system access plan for the CBTC system under complex conditions.The proposed plan can reduce both the safety risks and the commissioning time,and provide reference and practical experience for similar projects.