Abstract: During rectangular tunnel construction, the mechanisms of disturbance and damage to the surrounding strata remain unclear, often leading to engineering disasters such as surface collapse, deformation of adjacent buildings, and rupture of underground pipelines. Existing methods for predicting surface settlement also lack sufficient accuracy. To address these issues, a new method for predicting surface settlement is proposed using complex functions and the Maxwell-Betti reciprocal work theorem. First, two two-dimensional calculation models for rectangular tunnels under different stress states are established based on the reciprocal work theorem. Next, conformal mapping is used to transform the rectangular tunnel cross-section into a circle, allowing the derivation of a displacement formula for the tunnel body. The Sagaseta method is then improved to adapt to rectangular tunnel calculations. Using the reciprocal work theorem, a soil loss formula is derived and combined with the improved Sagaseta method to calculate the surface settlement induced by rectangular tunnel excavation. Finally, the effectiveness of the method is validated through four sets of numerical simulations and three sets of field monitoring data. The results show that the theoretical analysis is generally consistent with numerical simulation values and exhibits a high degree of agreement with monitoring data from the three projects. This method effectively adapts to surface settlement prediction for rectangular tunnels in various geological environments, providing a practical reference for engineering applications.