In this study, 3D elastic-plastic finite element analysis of a plate-fin structure with a fin offset was done by taking a unit cell consisting of two layers. The material of plate-fin was SUS316, and the multi-linear kinematic hardening model of Ohno and Wang was employed as the constitutive model of plasticity of this material. The unit cell was subjected to either monotonic or cyclic loading at 600℃, along with a differential pressure between the two layers. The periodic boundary condition was imposed on the opposed surfaces of the unit cell. It was thus found that the plate-fin structure exhibits significant anisotropy in the overall deformation as well as considerable compressibility in the layer-stacking direction. It was also found that the local strain range in the fin is several times larger than the overall strain range of the unit cell.