Abstract: Based on the structure characteristics of sheet to tube joined by spot welding,a welding system with servo gun was established.Due to large deformation of the weldments dur-ing the sheet to tube welding stage and unreliable ring nugget af-ter welding,a new method was investigated to increase the weld quality based on the electrode force change.The effects of varia-ble electrode force on weld tensile-shear strength and weld de-formation were researched.The results show that the weld strength can be increased and weld deformation can be decreased by adjusting the electrode force in welding process.Comparative-ly,the change of electrode force during holding stage has less in-fluence on weld quality.The studies can contribute to develop welding parameters for sheet to tube joining and to promote the wider application of single sided spot welding in the assembly of auto body.