To investigate the distribution pattern of additional stress fields induced by foundation pit excavation in layered ground, this study comprehensively considered the stratification characteristics of the foundation and non-limit state earth pressure. Based on layered elastic theory, an analytical solution for the additional stress at the axis of an adjacent tunnel was derived. Validation against the homogeneous Mindlin solution, Boussinesq solution, and field measurement data confirmed the method’s rationality. Results indicate that excavation-induced tunnel additional stresses exhibit an upward convex distribution along the tunnel axis. Increasing the horizontal distance between foundation pit and adjacent tunnel significantly reduces horizontal additional stresses on the tunnel. Conversely, increasing excavation depth and foundation pit shape coefficient nonlinearly increases the maximum horizontal additional stress. Incorporating non-limit state earth pressure yields additional stress fields at identical locations that better align with engineering reality, while calculations ignoring non-limit state earth pressure are conservative. The findings provide theoretical references for assessing tunnel service conditions in actual engineering projects.