Abstract: A calculating method for optimizing of the cross sectional shape of a subterranean tunnel and its application have been studied in this paper. The characteristic dimension of cross section of the tunnel has been taken as the design variable, while the total failure area within adjoining rock as the objective function and the area of water carrying section required as the restraint condition. The non linear optimization problem with constraint has been solved by use of the sequential unconstrained minimization technique (SUMT). The cross section of tunnel of a proposed project has been optimized and analyzed. And the result obtained is reasonable.