Abstract: Based on the biparametric equation for shape of rapture surface,according to the limit equilibrium principle and Mohr-Coulomb nonlinear criterion,the ultimate pullout force of prestressed cables could be calculated by the derived equation which considered the shapes of rapture surface,rock types,grouting pressures,grouting materials,unconfined compressive strength of rock and weathering degree.At last,a case of the ultimate pullout force for two type of rapture surface was given by using a nonlinear SQP algorithm and the relation between the nonlinear parameter and the ultimate pullout force was analyzed.The theoretical values agreed with the measured values from the field test.