Based on the nonlinear Mohr Coulomb strength criterion and the upper bound limit theory，a new formula for calculating the stress in the surrounding rock of shallow-buried small spacing tunnel was derived. The optimization calculation was conducted by using the fmincon function in MATLAB software. The upper solution of the stress in surrounding rock under the failure mode was obtained. The calculated values were compared with the results by the standard suggested method. The results show that the calculated value of the upper bound analysis is close to that of the standard suggested method， which verifies the proposed calculation method. With the increase of the coefficient m，the scope of soil failure on both sides of the shallow-buried small spacing tunnel increases gradually，the stress in surrounding rock also increases gradually，and the growth rate has a decreasing trend.