To overcome the inefficiency of existing numerical algorithms in calculating the contact slip law of complex fracture surfaces, a new numerical calculation algorithm was proposed by adoption of the idea of boundary element method. In this algorithm, all nodes were located at the boundary of rock blocks, and the interaction force between rock blocks and the displacement of rock blocks were calculated by using the explicit differential method. The algorithm was validated by two simulation experiments, i.e. “ball sliding on paraboloid” and “dumbbell on the inclined plane”. The results show the algorithm can accurately describe the contact between objects and accurately calculate the normal displacement between blocks. Besides, the algorithm can accurately judge the "sliding state" and "stable state" of the object. The error between the numerical and analytical results of friction force is less than 10?10. When calculating the variation of bearing capacity during slip of fracture surface, the calculation results of the new method are consistent with the results of the finite element method, but the calculation efficiency of the new method is significantly improved.