Abstract: In sheet-tube indirect spot welding, it is difficult to assure welding quality because the welding deformation is too large.The expansion and welding deformation were investigated and the influence of different welding parameters (welding current, electrode force and welding time)on indirect spot welding process was analyzed through electrode displacement.The experiment result shows that the course of the expansion and welding deformation are coupled to each other in the welding stage;in the holding stage, welding deformation gets larger under the ailion of applied electrode force.Maximum welding deformation of sheet-tube indirect spot welding process is almost linear with electrode force and input welding energy.Ladder-type occurs in the electrode displacement curve when the expulsion happens, so the expulsion can be judged according to the slope coefficient of electrode displacement.The result provides a theoretical guidance for on-line monitoning and control of welding quality in sheet-tube indirect spot welding process.