Simplified one-step analysis of sheet metal forming is increasingly used in automobile industry since it can promptly predict the formability of final parts during the early design stage. This method is however based on an implicit static algorithm and suffers from convergence problems because of its strong nonlinearity. A remedy is a robust initial guess method for these convergence problems. This paper proposes a new initial guess method for one-step analysis. The blank mesh as an initial guess is obtained from inverse elastic deformation based on the known shape of a final three dimensional part. An accurate incremental simulation is too time-consuming and lack of tool information during the design stage to be achieved. We applied one-step analysis to obtain the changed properties of stamped vehicle parts resulted from forming process in order to consider forming effects in the side impact analysis of ULSAB-AVC. The mesh from a crash model is used as input data. For treatment of vertical and undercutting walls we also propose a new technique which has proven to be essential and efficient when dealing with complicated parts. It is concluded that this new initial guess method and the treatment of vertical and undercutting walls play an important role in obtaining a good initial guess for auto-body stamping parts. It is well demonstrated that the one-step analysis is a simple and effective method to generate the stamping results for crash simulation with forming effects.