Stainless steel has many advantages such as excellent durability, ductility and corrosion resistance. Recently, the use of stainless steel has been increased in a variety of structural members and industrial fields. But, stainless steels are not included is the structural materials of Korean building standards and corresponding design standards are not specified. In this paper, finite element analysis has been performed to investigate the ultimate strength of single shear duplex stainless steel (STS329FLD) four-bolted connection with extended variables. As a result, strength reduction ratio by curling was estimated quantitatively.