<p>Underground group tanks (UGTs) for edible oil offer benefits in land conservation, ecological sustainability, and oil quality preservation. However, ensuring their structural integrity is a critical concern. This study investigates the mechanical behavior and stability of tank walls with inner steel plate lining in the empty tank, employing both full-scale tests and numerical simulations. Parameters such as internal forces, circumferential deformation, and wall stability under earth pressure were comprehensively examined. Findings reveal that the circumferential internal forces in walls proximal to the junction are more influenced by the junction and adjacent tank walls than those in walls located further away. The numerical results deviate by only 7.7% and 13.3% from the experimental results, verifying the efficacy and accuracy of the numerical model employed. Additionally, it was determined that for tank walls with heights below 5 m, the internal force can be computed using retaining wall force calculations; for greater heights, arch action force calculations are more suitable. Based on stability analysis, a formula for assessing the stability of double-layer, heterogeneous material group tank walls under earth pressure is introduced. It is advised that the thickness of the concrete tank wall should exceed 150 mm to ensure structural stability. These findings offer valuable insights into the rational design of UGTs.</p>