Tridimensional problems of rockmass involve a large number of calculations and are complicated to deal with using mathematical methods, and often with poor precision. The conventional alternation method, which is usually used to solve plane nonlinear problems, gives no convergence solutions to tridimension tridimensional ones. To simplify calculations, constitution equations for rockmass are used to modify solutions to tridimensional elastoplastic problems through primitive stfess increment method of boundary element. A stress calibrating method is proposed for calibration of deviation of yield point from yield plane due to multiple alternations.