This　paper　presents　an　improved　level　set　method　for　topology　optimization　of　geometrically　nonlinear　structures　accounting　for　the　effect　of　thermo-mechanical　couplings.　It　derives　a　new　expression　for　element　coupling　stress　resulting　from　the　combination　of　mechanical　and　thermal　loading,　using　geometric　nonlinear　finite　element　analysis.　A　topological　model　is　then　developed　to　minimize　compliance　while　meeting　displacement　and　frequency　constraints　to　fulfill　design　requirements　of　structural　members.　Since　the　conventional　Lagrange　multiplier　search　method　is　unable　to　handle　convergence　instability　arising　from　large　deformation,　a　novel　Lagrange　multiplier　search　method　is　proposed.　Additionally,　the　proposed　method　can　be　extended　to　multi-constrained　geometrically　nonlinear　topology　optimization,　accommodating　multiple　physical　field　couplings.