Basement structures offer an effective solution for maximizing land use in densely populated urban areas. These structures require careful consideration of various factors, including soil behavior, surrounding conditions, and the design of retaining walls capable of withstanding lateral earth pressures. This study investigates the impact of an adjacent basement by varying both the distance and depth relative to an existing basement structure. The analysis was conducted using the finite element method with the aid of Midas GTS NX software. Results indicate that increasing the distance between basements reduces the lateral earth pressure on the existing structure’s retaining wall. Conversely, when the adjacent basement is positioned at a lower elevation than the existing one, the lateral earth pressure on the upper portion of the wall increases. However, this vertical influence is less pronounced compared to the effect of horizontal distance, suggesting that spacing plays a more critical role in lateral pressure distribution.