In this paper, a 3D numerical simulation method was put forward by coupling magnetic-structural fields, and its reliability was verified through comparing with the experimental data offered by Suzuki. According to the characteristics of electromagnetic expansion of metal tube, this simulation method was used to analyze the uniformity of tube expansion when the length of tube was less than that of the coil. Meanwhile, a curve of homogeneity of electromagnetic tube expansion with different aspect ratios (ratio of length to diameter) of tube was given based on the criterion of uniformity on deformation at the condition of specific parameters presented in this paper. By analyzing the mechanical characteristics of tube expansion, a length range of tube was found where the tube deformed uniformly. The results derived from this paper provided a good guidance for optimization design of electromagnetic ring expansion experiments which will be conducted on and this could ultimately promote the application of electromagnetic forming.