To ensure the stability of the laser communication system under complex dynamic loads, an off-axis dual-mirror optical antenna system was developed. Thermal-mechanical coupling analysis and wavefront aberration evaluation were conducted to predict the aberration under dynamic conditions and verify structural reliability. Based on D'Alembert’s principle, an acceleration–temperature gradient coupling model was constructed, and a mapping between rigid body displacement and wavefront error was established. Simulation results indicate that the maximum deformation under composite loading is 0.065873 mm, and the RMS wavefront error increases from 0.047λ to 0.068λ, remaining within the RMS < 0.1λ design threshold. The initial wavefront RMS measured by the ZYGO interferometer is 0.052λ, deviating from the simulated value of 0.047λ by only 0.005λ. This validates the model’s accuracy and offers theoretical and engineering support for high-precision optical design in space-based laser communication systems.