To reduce the iron loss of a reactor stacked with non-oriented steel plates, we have proposed the method of loss reduction improving the iron core configuration using the magnetic field analysis taking account of the laminated structure by the homogenization technique. In this paper, the iron loss reduction method is expanded to a reactor stacked with grain-oriented steel plates. The magnetic field analysis taking account of the laminated structure and steel plate anisotropy using homogenization technique is developed. The flux concentration due to the laminated structure, steel plate anisotropy, and joint between the leg and yoke of the reactor is analyzed and relaxed by the improvement of the core and joint configurations. It is shown that the iron loss can be about 36% reduced by the improvements.