The interdecadal migration of the southernmost latitude of the coastal Oyashio is investigated using a simple layered model. Being influenced by the changes of the Aleutian low which shows two dominant oscillations with bi-decadal and penta-decadal periods, the southernmost latitude gradually migrated southward from the 1970s to the early 1990s with less bi-decadal signals. The westward baroclinic Rossby waves on the be-decadal period could be attenuated effectively by the local wind stress anomalies which changed their signs on the characteristics of the Rossby waves. As a result, only the penta-decadal signal can survive and reach the western boundary region, and the coastal Oyashio can be affected. In the analyzed period from the 1970s to the 1990s, the transient responses of the North Pacific ocean to the interdecadal changes of the Aleutian low could play a role in cutting off the bi-decadal signals.