In the current construction industry, exterior wall external insulation systems are widely used but suffer some obvious weathering problems such as deformation, drop in thermal insulation, and fracture of the surface layers. To investigate the weathering performance of an exterior wall external insulation system from the perspective of wall temperature stability, ABAQUS finite element software was used to establish a three-dimensional transient thermal-structural coupling model of the effect of paint finishes, with added adhesive powder polystyrene particle insulation slurries, on exterior wall external insulation. Numerical simulation analysis was carried out to calculate the real-time temperature field, thermal stress, and displacement distribution of different functional layers under heating-cooling cycles. Results show that during the heating-cooling cycles, the temperature difference in the coating layer is the greatest, that in the interior layer is the smallest, and the daily change is within 2℃. The rate of temperature change in the insulation slurry layer in the thickness direction is higher than that in the other materials. The coating layer is subjected to tension-compression cycles with tension at low temperatures and compression at high temperatures. The inner surface of the primary wall is always under compression throughout these cycles and the stress variation in the primary wall is small. By comparison, the stress in the interfacial mortar layer is large and that in the insulation slurry layer is almost zero. The maximum displacement in the thickness direction occurs in the insulation slurry layer.