Based on the beam model under the action of uniform load and concentrated force in structure stability theory, a simply supported beam model under the action of trapezoidal load was established and its flexural equation was calculated. And shallow-buried bias tunnel was treated as simply supported beam under the action of trapezoidal load, the maximum bending moment of simply supported beam was computed by the calculated flexural equation. Under the condition of the bending stress not beyond the allowable bending stress, the minimum safety thickness of overlying rock mass on hole crest was obtained on the basis of stress calculation formula and strength conditions. Before the shallow-buried bias tunnel excavation, it can be judged through the minimum safety thickness calculation whether the designed overlaying rock thickness meets the safety requirements or not, so as to avoid engineering accidents.