The shield type selection and ground deformation rule of a twintube Metro tunnel on No. 1 line of Lanzhou urban rail transit in sandy cobble strata are studied. The mathematic calculation model of torque and thrust of shield is introduced and the calculation result is used in the field tunneling and the 3D finite element simulation, the range, characteristics and variation rules of the settlement trough and the range and rule of the influence of the ground deformation in transverse direction and longitudinal direction induced by shield boring are analyzed. The study result shows that: 1) The closer to the ground surface, the smaller the disturbance effect of the tunnel boring on the settlement trough; 2) The asymmetric feature of the ground settlement is obvious; 3) Due to the superposition of the disturbance effect of the ground in horizontal direction, the ground is subject to shear deformation, therefore necessary protection measures should be taken; 4) The monitoring data are in good agreement with the numerical simulation result, which shows that the construction methods adopted are rational and the settlement has been brought under effective control. 