The heat exchanger has grooves inside the tube to improve heat transfer efficiency. However, the heat exchanging efficiency is reduced due to the deformation of the grooves in the tube. Therefore, the purpose of this research is to design a tube expander to reduce the plastic deformation of the inner groove height of heat exchanger tubes during tube expansion process. The tube inner groove deformation was calculated by elastoplastic finite element analysis under the boundary conditions with the tube end fixed and a friction coefficient of 0.22 between the tube and tube expander. The deformation of the grooves in the tube expanded by the expander with a radius of 7.9 mm was reduced by about 25% compared to the expander with a radius of 5.3 mm. Based on the results, we plan to design a shape of the tube expander to further minimize deformation of the tube inner grooves in tube expansion.