Abstract: In this paper, a theoretical model of the optical transmission was established to study the optical distortion resulted from the dynamic thermal effect. Numerical simulation shows that the optical distortion is mainly caused by the uniformity deformation of the end plane. In order to analyze how the dynamics thermal effect worked on the energy output, numerical calculation on the process of energy conversion in unsteady state was done, and the simulated result matched the experimental result precisely, which also showed that Boltzmann distribution of particle number was not the main reason for the rapid decline of output power when the temperature was under 400 K. The main reason of the rapid decline of output power was the deflection dissipation resulted from dynamic optical distortion.