Formation of a narrow magnetic domain wall is demonstrated by micromagnetics simulations. It is found that the domain wall width can be shrunk in a local exchange coupled system. The local exchange coupled system means that only a part of a ferromagnetic layer has an exchange coupling with another ferromagnetic layer. The system can be considered as two parts in the lateral dimensions: one is an exchange coupled region and another is a free region. Since the two regions have quite different local switching fields, the domain wall will be formed at the interface between the two regions at moderate field ranges.