Nuclear materials are exposed to high temperature, high pressure and strong irradiation for a long time, and are subjected to strong neutron irradiation, which will produce a large number of point defects under the action of cascade collision, and then form radiation voids. Irradiation swelling caused by irradiation voids is responsible for the failure of austenite steel serve in the reactor core. The external stress introduced in the process of material processing and service and the elastic stress field generated by crystal defects such as dislocation have an important influence on diffusion and phase transformation. The phase field method at mesoscale can not only couple the physical fields such as temperature, irradiation and stress, but also simulate the dynamics and morphology evolution of the microstructure of materials during irradiation. A mesoscale phase field model coupled with rate and micro-elastic theory is used to survey the stress effects on void microstructures for Fe-Cr austenite; the global applied stress and the local dislocation stress field are considered. The applied stress promotes vacancies aggregate, nucleate, and growth, and the voids evolve into fusiform eventually. Voids in the stressed state have a larger size and lower density compared with a stress-free state. The larger the applied stress, the larger the average size and volume fraction, the smaller the number, and the more significant the morphology reconstruction is. The local elastic stress field of dislocation absorbs vacancies to reduce the elastic energy, and the concentrated vacancies accelerate the voids preferentially nucleate and grow around the dislocation. Compared with the dislocation-free system, the voids are fine and denser when dislocations exist; but the volume fraction and the morphologies of voids persist. In contrast, the applied stress should probably cause server swelling than dislocations in Fe-Cr alloys. The studying benefits the properties evaluation of in-core reactor components.