The　characteristics　of　seismic-induced　inelastic　torsion　in　frame-bent　structures　in　the　main　buildings　of　large　thermal　power　plants　are　investigated.　On　the　basis　of　a　real　engineering　design　scheme,　nonlinear　finite　element　models　for　seismic　time-history　analysis　are　established　in　SAP2000.　The　variation　of　structural　lateral　displacement,　nonlinear　torsion　and　the　internal　forces　of　main　structural　elements　are　analyzed.　It　is　revealed　that　the　buckling　of　the　steel　braces　is　the　main　reason　for　the　nonlinear　torsion　and　its　rapid　increment.　The　presence　of　nonlinear　torsion　contributes　to　a　distortional　displacement　field,　and　could　be　harmful　to　the　key　elements　of　low　ductility　that　connect　the　roof　truss　or　crane　hoist　etc.　to　the　structure.　The　ratio　of　torsional　displacement　to　lateral　displacement　defined　in　some　standards　is　studied　to　find　that　it　hardly　suites　to　the　situation　of　inelastic　torsion.　This　phenomenon　and　its　reason　are　analyzed.　Some　technical　suggestions　to　decrease　the　nonlinear　torsion　are　put　forward.　©　2017,　Engineering　Mechanics　Press.　All　right　reserved.