<p>We propose a polyhedral cell-based smoothed finite element method for thermally nonlinear thermo-mechanical coupling problems. A discretization method for cell-based smoothing domains is designed to construct tetrahedral cell-based smoothing domains based on polyhedral background elements. On this basis, the method transforms the volume integrals over each polyhedral element into surface integrals along its tetrahedral cell-based smoothing domains. The gradient smoothing technique eliminates the need for shape function derivatives by requiring only shape function values along the segments of the cell smoothing domains. This approach avoids the complexities of coordinate mapping associated with traditional finite element methods and eliminates the difficulty of constructing shape functions for polyhedral elements. It also naturally ensures the positivity condition in a normed <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\({\mathbf{G}}_{h}^{1}\)</EquationSource> </InlineEquation> space without additional stabilization. Numerical results show that the method yields high-accuracy solutions and effectively handles heterogeneous media and stress concentrations.</p>