A finite element model of the side hole flanging for propellant tank parts in the electromagnetic forming process was established based on the multi-physics coupling module and the loose coupling method, and the distribution of the electromagnetic force, stress, strain and thickness of the blank and their variations with time were revealed. Furthermore, the process parameters of the discharge voltage and the coil inner diameter were optimized. The analysis results show that the stress and strain of blank are bigger at the round corner area with a larger thickness reduction and a larger residual stress at the round corner area. With the increase of the discharge voltage, the deformation of blank increases, while the thickness reduction increases correspondingly. As the coil inner diameter increases, the maximum clearance and the maximum angle between die and blank, and the minimum thickness of the blank decrease firstly and then increase. Finally, the optimum values of the discharge voltage and the coil inner diameter are 40 kV and 40 mm respectively.