To analyze large-scale fracture mechanics problems effectively, we apply the partitioned iterative coupling algorithm which has been successfully utilized for multi-physics coupling problems. In the algorithm, the analysis domain is first decomposed into two domains. The one domain contains a crack, while the other does not. The two domains are analyzed separately and alternately with assumed boundary conditions on the boundary between the two domains. By updating the assumed boundary conditions repeatedly, the converged solution is finally obtained. In crack propagation analyses, this coupling iteration is performed at each crack propagation step. In a numerical experiment of an edged crack tension plate model of 1.96 million degrees of freedom, stress intensity factors are computed 4.52 times faster than using a conventional finite element method. This is because, in the partitioned iterative coupling algorithm, the stiffness matrix on the domain far from the crack is constant through the whole crack propagation analysis.