The object of research is thermomechanical behavior of polymer composites based on thermoset epoxy binder and T23 fiberglass fabric. In the operating conditions of industrial chimneys, which include high temperatures, long-term operation, cyclic mechanical and temperature impact, prolonged thermal aging, it is yet to be determined. One of the major concerns is the definition of thermomechanical properties. This work is devoted to the development of the finite element (FE) model which should allow us to predict properties of composite and could be used for calculations of composite structures. Method. Tensile tests were conducted in the specially manufactured testing chamber, which allowed us to acquire the modulus of elasticity and coefficient of thermal expansion (CTE) of both polymer and composite. Then, the FE model was developed based on the previous polymer’s FE model. Results. The proposed FE model showed satisfying results and predicted modulus of elasticity and CTE of polymer composite with high accuracy. The model then was tested on another data from a different batch and appeared to be accurate. Then the model was compared to traditional rod and shell calculations of temperature stress and the results were similar, confirming the adequate stress-strain state of the modeled structure.