Abstract: This article uses finite element simulation to study the working principle of the fieldshaper. It analyzes the magnitude and waveform of the coil current discharged in MPW, the distribution of magnetic field and electromagnetic force during the welding process, the structural strength of the fieldshaper and the size of the Al tube electromagnetic diameter reduction are compared. The results demonstrate that the fieldshaper utilizes the height difference between the inner and outer sides of the structure to facilitate the flow of induced current from the larger outer surface to the smaller inner surface, thereby achieving the convergence of induced current. The improvement of magnetic field distribution by the fieldshaper is positively correlated with the inclination angle α of its inclined wall, the performance of the vertical fieldshaper is higher than that of the conventional fieldshaper and lower than that of the curved fieldshaper. The shape of the cross-section also has a certain effect on its performance, curved fieldshaper structure with the α angle equal to 0 has the best performance, with a 12% increase in the magnitude of magnetic induction intensity in the welded region and a 24.9% higher deformation of the Al tube electromagnetic diameter reduction compared to the conventional fieldshaper, which is more commonly used today. The three types of fieldshaper have small differences in structural strength, all of which can ensure the stability of welding. This paper can provide a certain reference for the design of the fieldshaper structure.