FLAC3D model is established and numerical analysis is made on a pair of adjacent tunnel tubes of Shenzhen Metro, so as to study the ground surface settlement of adjacent tunnel tubes caused by different excavation sequences and, in the end, to obtain the optimal excavation sequence. In the study, advanced supporting of the surrounding rock is simulated by equivalent reinforcement rings. The following conclusions are drawn by study on the ground surface settlement pattern in the vertical and horizontal directions caused by different excavation sequences, as well as on basis of the theory and field monitoring data: 1) If the preceding tunnel tube is excavated by top heading and bench method and the following tunnel tube is excavated by CRD method, it is better that the following tunnel tube should be excavated in upperlower sequence and that the part close to the preceding tunnel tube should be excavated first; 2) The influence of the excavation sequence on the ground surface settlement reduces as the distance between the twin tunnel tubes decreases; 3) The reinforcement ring has obvious effect in retraining the differential settlement of the adjacent tunnel tubes; 4) The top heading plays a key role in controlling the ground surface settlement, with the maximum ground surface settlement occurring at the position close to the centerline of the following largespan tunnel tube.