The finite element numerical simulation of the coupled structure-electromagnetic fields was carried out based on LS-Dyna platform for the electromagnetic constriction process of aluminum/steel bimetallic tube, aiming to guide actual precision forming process of bimetallic tube. The influences of the inner and outer tube wall thickness ratio, the inner and outer tube gap, discharge voltage, and elastic mandrel on forming quality were studied. Results show that small wall thickness ratio caused the weak connection of the tubes, while large wall thickness ratio led to the depression of the inner tube and the crack of the outer tube. As the discharge voltage increased or the distance between two tubes decreased, the constriction impact force of the outer tube was increased, which resulted in a drastic increase in the circumferential stress of inner tube and the occurrence of instability and wrinkling, as well as the crack of the outer tube. On the contrary, with the discharge voltage decreased or the distance between the two tubes increased, the constriction impact force of the outer tube was decreased, and the inner tube could not bear an effective deformation and springback process, leading to smaller effective connection area between the two tubes. The elastic mandrel could restrain macro-defects such as cracking at a certain extent, and appropriately increase the springback of inner tube. Lastly, the electromagnetic forming rules and defect control theory were obtained based on theoretical calculation and finite element simulation. With the purpose of increasing the length of effective connection area and reducing macro-defects, the research parameters were optimized, and it was found that the forming quality is the best when the inner tube wall thickness remains 1 mm, outer tube wall thickness is 1.5 mm, the gap between the tubes is 0.7 mm, and discharge voltage is 50 kV.