Abstract：Based on the unified strength theory，the limit equilibrium principle and the shape of rapture of surface，a formula，which takes into account the shape of rapture surface，dip angle of cable，grouting pressure，varieties of rocks，are deduced. In order to validate the practicability of the calculation formula，by taking different influential factors into account，a comparison between the theoretical and actual data is made in soft rock and hard rock. The results reveal that，with the increase of the coefficient of weight b，the ultimate bearing capacity of cable increases too，yet the shape of fracture plane doesn¢t change；the ultimate bearing capacity of cable depends much more on the boundary strength between grouting and rock，or grouting and cable than that of the fracture plane of cone. In soft rock，the ultimate bearing capacity of prestressed cable，less influenced by the grouting pressure，depends mainly on the boundary strength between rocks and grouting. In hard rock，the grouting pressure plays an important role on the ultimate bearing capacity and the height of rock cone. When the grouting pressure increases，the ultimate bearing capacity and the height of rock cone increase too. In technical application，by utilizing the intensity parameter formula of unified strength theory，the intensity parameters of soil and rocks corresponding to the coefficient of weight b which contains the contribution of the second principal stress，can be calculated.
