Fe-Cr-Co alloys are becoming important as half-hard magnet which can be subjected to plastic deformation process for their novel applications including non-contact electromagnetic brake because of its large hysteresis loss. Its magnetic hardness depends on the modulated structure formed by spinodal decomposition. It is important to clarify the effect of plastic deformation on the spinodal decomposition for optimizing the heat treatment after plastic deformation process. In the present study, we examined the spinodal-decomposed structures in Fe-Cr-Co sheets cold-rolled to 25% reduction and that without rolling to clarify the influences of cold rolling. Also, spinodal decomposition under the presence of dislocation structure have been simulated by phase field method for the case with the presence of dislocation cell boundary with a high in-plane solute diffusivity at various migrating speed. It has been found that the spinodal decomposition is accelerated around dislocation owing to the elastic field and higher diffusivity, which results in inhomogeneous microstructure with various wave length of modulation. The existence of dislocation enhances the initiation of phase decomposition and the growth particles. The decomposed structure greatly depends on the in-plane solute diffusivity and migrating speed of the dislocation cell boundary.