This paper provides benchmark solutions of space steel frames using second-order distributed plasticity analysis. The majority of available benchmark solutions of steel frames in the past were only of two-dimensional frames. Therefore, three-dimensional benchmark solutions are needed to extend the knowledge of this field. Details of the modeling including element type, mesh discretization, material model, residual stresses, initial geometric imperfections, boundary conditions, and load applications are presented. Case studies of Vogel's portal frame and space steel frames are performed. The ultimate loads obtained from the proposed analysis and Vogel agree well within 1% error. The ultimate loads of the space steel frames obtained from the proposed analysis and experiment compare well within 35% error. The benchmark solutions of the space steel frames are useful for the verification of various simplified second-order inelastic analyses. It is observed that the load carrying capacities calculated by the AISC-LRFD method are 2531% conservative when compared with those of the proposed analysis. This difference is attributed to the fact that the AISC-LRFD approach does not consider the inelastic moment redistribution, but the analysis includes the inelastic redistribution effect.