Abstract: In resistance spot welding,a strong magnetic field is generated due to a high current applied.A theoretical analysis on electromagnetic force caused in the process of resistance spot welding was carried out based on stationary machines by simplifying the elec trode arms and electrodes as electric conductors,and the electromag netic force was measured by means of a middle-frequency DC ma chine.The results indicate that the electromagnetic force has an effect on reduction of the electrode force,i.e.counteracting the electrode force.The electromagnetic force is mainly affected by the welding current and electrode-arm open depth.It is direct proportional to the square of the welding current and inverse proportional to the elec trode-arm open depth.Therefore,the effect of electromagnetic force must be considered when the electrode force is set or measured in the real production