The low cycle fatigue test of IF steel was controlled at 0.6%, 0.4%, 0.2%, and 0.1% strain amplitude until the specimens cracking. After 10000 cycles at 0.4% strain amplitude, changed the strain amplitude from 0.4% to 0.2%. We chose the steps of the low cycle fatigue test under reducing amplitude at 1000, 10000, and 20000 cycles. In addition, after 10000 cycles at 0.6% strain amplitude, changed the strain amplitude from 0.6% to 0.2%. We chose the steps of the low cycle fatigue test under reducing amplitude at 3000, 20000 and 100000 cycles. Then we used electron microscope to observe the dislocation structure, and knew the dislocation morphology of evolution process under reducing amplitude. The dislocation structure evolution of IF steel at low strain amplitude (0.1%, 0.2%) during low cycle fatigue developed the loop patches, dislocation walls, and dislocation cells step-by-step by increasing fatigue cycles. However, the dislocation structure evolution would be changed in the low cycle fatigue under reducing amplitude. We could observe that the dislocation cells were broken to the loop patches in different form. Attest to the dislocation morphology was changed under reducing amplitude. After 10000 cycles at 0.4% strain amplitude, change the strain amplitude from 0.4% to 0.2%., we could observe that the dislocation cells were broken to the loop patches and vein structure. And after 100000 cycles under changed loading amplitude from 0.6% to 0.2%, large area of open domains and some loop patches can be observed.