Abstract: 20G steel tube sizing process with electromagnetic bulging had been analyzed by axial magnetic field strength. The effects of coil inductance,discharging voltage and times on the sizing precision of the tube ends were analyzed with deformation of the tube end as evaluating indicator. The result indicate that coil inductance and discharging times had effects on sizing precision,but the discharging voltage was the primary factor for the sizing precision. In order to raise the sizing precision,the experiment obtained the optimize craft and parameter.