Tensile residual stress of resistance spot welded structures increases the maximum stress and tends to reduce fatigue strength. Accordingly, the welding process must be optimized to minimize the tensile residual stress. This paper presents residual stress obtained from electrical-thermal-structural analysis and the parameters that affect residual stress. First, assuming the bilinear isotropic material in elastoplasticity, simulated residual stresses have good agreement with the measured data when the hardening tangent, as a parameter, is assumed to be 1% of the elastic modulus. Another result is that the contour of residual stress around a spot weld can be drawn within the weld lobe, and residual stress can be represented with welding conditions on the three-dimensional regression plane. Finally, equations for residual stress are developed in terms of welding conditions and are used to find welding conditions that minimize residual stress.