<p>The aim of this study is to determine the influenced zone of deep excavation, and provide a simplified prediction method for the underlying tunnel displacement according to the actual influenced zone where it locates. Based on the statistics of 33 collected case histories, 279 finite element method numerical models are established to analyze the underlying tunnel displacement behaviors induced by deep excavation, considering the factors of excavation depth and tunnel position. Then, based on an analysis of the tunnel displacement isogram, according to the 3-level tunnel displacement control standards, the influenced zones of deep excavation on the underlying tunnel are categorized, and the scope of the influenced zones is characterized according to their features. Next, the effect of excavation depth on the scope of influenced zone is studied, and the influenced zone under any excavation depth conditions and a simplified prediction method for the underlying tunnel displacement are proposed. Furthermore, the reliability of the proposed method is verified by comparing with the case histories. And finally, the proposed method is applied to a practical project, and the application effect is evaluated. The results show that the range below the base slab can be divided into “primary,” “secondary,” “general,” and “weak” influenced zones induced by deep excavation. The scope of influenced zones can be simplified as a right-angled trapezoid shape, the isoline of tunnel displacement can be simplified as a straight line, and by defining two parameters on the line: depth coefficients <i>N</i>₁ and <i>N</i>₂, the scope of influenced zones can be easily determined. In practice, using the proposed method to predict the tunnel displacement in the influenced zone and take targeted measures can effectively reduce the effect of deep excavation on the underlying tunnel.</p>