Due to the complex coupling effect of the double-line tunnel, the surface settlement pattern caused by the shield construction is extremely complicated, so it is more difficult to predict the surface settlement accurately. Based on Peck's formula and Chapman's correction parameter, the prediction formula for surface settlement of the twin tunnel was established through the empirical quantification of the parameters considering the construction influence of the prior tunnel and the relative position relationship of the double-line tunnel. In addition, the applicability of the formula in different soil layers and the range of parameter values were discussed by relying on the Suzhou Railway Line S1 Project, and on this basis, the numerical simulation of the double-line tunnel shield construction was carried out by using PLAXIS 3D finite element software. The results show that the surface settlement values calculated by applying the modified formula are in good agreement with the numerical simulation and field measurement results for shield construction in soft ground. The established formula takes into account the location information of the twin tunnel, which can quantitatively reflect the influence of the tunnel depth and the spacing of the double-line tunnel on the surface settlement, and the settlement curve fitted by the modified formula shows a normal distribution. The research results can provide a reference for the calculation of settlement in double-line tunnel shield construction in soft soil areas.