Abstract: Sudden ground surcharge may impose additional loads on existing metro shield tunnel segments, potentially leading to deformation or structural damage. Investigating the mechanical response of existing segments under surcharge conditions is crucial for optimizing segment design. This study focuses on a running tunnel section of Xi′an Metro Line 9, employing a similarity model test with a geometric scaling ratio CL = 40. Based on 3D printing technology and artificial preparation method of collapsible loess, this study investigates the surrounding rock pressure and segment deformation patterns under surface surcharge conditions, with comprehensive consideration of influencing factors including surcharge magnitude, tunnel burial depth, and loading position. A modified calculation method for surrounding rock pressure based on the surrounding rock pressure amplification coefficient β and transfer coefficient η was proposed. Additionally, a four-zone influence classification system is established under surface surcharge conditions, along with segment displacement control criteria for different surcharge magnitudes and positions. The results demonstrate that the surrounding rock pressure of the tunnel increases linearly with the surcharge magnitude, while the increment of surrounding rock pressure generally exhibits a decreasing trend with increasing eccentric distance. When the surcharge is positioned at 0.5D and 1.0D, the reduction in surrounding rock pressure on the eccentric side is significantly smaller than that on the non-eccentric side. At a surcharge position of 1.5D, the variations in surrounding rock pressure on both sides of the tunnel become nearly identical. Furthermore, the influence of surface surcharge on tunnel surrounding rock pressure relatively diminishes with increasing tunnel burial depth.