The necking limit of a sheet metal under stretch bending is much larger than that in uniaxial tension because of the existence of a strain gradient. This paper discusses the influences of materials’ workhardening and stretching force on the onset of necking under in-plane stretch-bending of sheet metals based on the experiment and its corresponding finite element (FE) simulation. To represent the workhardening of the material in the simulation, a combined Swift-Voce hardening model with a weighting coefficient μ was used. The anisotropy of sheets was considered using a sixth-order polynomial yield function. The results of experiment and simulation on three types of high-strength steel sheets are presented. From these results, it was found that the necking is more likely to occur for low workhardening materials under large stretching force, although the stretching can prevent the buckling of the sheet.