Dynamic crack-growth model, which is based on the crack-tip local fracture stress criterion and takes account of the effect of unbroken side-ligaments near the plate surfaces and crack-bowing inside the plate, is extended for simulating crack-growth and arrest behavior in the duplex-type test. Different local fracture stresses for starter and arrester plate are assumed. Depending on the applied stress and temperature of the arrester plate, a crack continues to propagate or arrests in the arrester plate. Discrepancy of arrest toughness which was observed between temperature gradient-type and duplex-type tests is reproduced by the present model and its reason is explained by the different thickness and length of the unbroken side-ligament between the two types of the tests.