Abstract: Restricted by the topography, the Qingxiushan metro station of Nanning rail transit line 3 is built by open cut method for the upper part and mined method for the lower part. The lower mined tunnel is classified as the one in the transition zone from the shallow overburden to the deep overburden, and it′s significant for proper equivalent calculation of the upper open-cut excavated station hall to ensure structure safety of mined tunnel regarding structure design. The vertical pressure of surrounding rocks of the lower mined tunnel is 150.69 kN/m and the horizontal pressure of surrounding rock is 95.28 kN/m when the upper station hall structure is equivalent to soil body;the vertical pressure of surrounding rocks of the lower mined tunnel is 439.83 kN/m and the horizontal pressure of surrounding rock is 103.28 kN/m when the upper station hall structure is equivalent to additional load. The numerical calculation shows that the maximum safety factor is 60.29 (at haunch) and the minimum safety factor is 7.39(at bottom) when the upper station hall structure is equivalent to soil body; the maximum safety factor is 21.558 (at arch spring) and the minimum safety factor is 2.529 (at bottom) when the upper station hall structure is equivalent to additional load. It is suggested that it is proper for the upper station hall structure to be equivalent to additional load regarding the pressure calculation of surrounding rocks of the mined tunnel.