Development of technology has to offer several connection methods such as welding, sewing sheets, solder, … tothe owners of great industries. Each of these methods have advantages and disadvantages and their specificapplications. Mobarakeh Steel Company has used resistance welding to connect the coils of yarn sheet to maintain continuity of its production line. Although welding is one of the easy ways to connect the two sheets, but also has disadvantages. For example, hot and cold cracks created during the welding process, the sheets are prone to rupture.In addition, residual stresses from resistance welding, reduces the load carrying capacity of sheet and Accelerate the growth of cracks generated during resistance welding. In this project, in order to investigate effect of resistance welding on the failure of sheet, resistance seam welding has been simulated in the analytical software. This process is an electrical - thermal - mechanical - metallurgical process so failure Investigation is difficult by experiment. In this process, simultaneously applying heat and pressure cause the connection between the two sheets. Resistance welding is often done As spot welding therefore, most researchers have focused on resistance spot welding And simulation of resistance seam welding hasnot been done. To correct modeling of this process, resistance welding should be fully investigated. Contact surfaces treatment must be considered in order to correct modeling of resistance welding process. To simulate resistance seam welding process the element with temperature, displacement and electric potential degrees of freedom is required. because analytical software havnt element with temperature, displacement and electric potential degrees of freedom process simulation program has written in python language in abaquse. This program is doing thermomechanical and electrothermal analysis at time intervals 0.0007 sec. In each step of the simulation, Electrode moves forward 0.5 mm. In electrothermal analysis welded surfaces and contact surfaces can be found and these surfaces are introduced to model. Another task of this program is to apply the temperature field obtained from electrothermal analysis to the thermomechanical model . No similar work in resistance seam welding simulation has been done so validation of above program has been done by simulation of resistance spot welding and compare its results with results of other researchers. Simulation of resistance seam welding results showed that transverse residual stresses generated within the sheet is negligible in comparison with longitudinal residual stress. Finally, effect of deformation of sheet due to resistance seam welding on propagation of crack in the sheet has been studied by extended finite element method. Also to closer look on propagation of crack in resistance seam welded sheet, crack growth phenomena has been evaluated by simple tensile test. In order to observe the effect of resistance seam welding on crack growth in specimens, the initial cracks in various areas of the samples was created. Key words Resistance welding, Electrothermal, Thermomechanical, Residual stress, Fracture, Crack