Abstract: Aimed at addressing the complex force conditions, challenges to blasting and support in overlapping tun? nels with a minimum clear distance, a numerical simulation is carried out for lower tunnel tubes regarding five kinds of excavation spacing. The distribution features of the surface and crown settlements of two lower tunnel tubes for different excavation spacings are analyzed based on the Zaoshanlu-Lichun running tunnel project of the Qingdao metro, and the stability of the rock mass and construction costs for different excavation spacings are studied by numerical calculations and theoretical analysis. The results show that the surface settlement, vault settlement and volume of the plastic zone will decrease gradually with an increase of the excavation space between the parallel tunnel tubes, along with the extension of construction period and the increasing of expenses; so a reasonable excavation spacing between the left and right tube is 25~35 m determined by the multi-index comprehensive assessment meth? od.