The supporting way is crucial to the deformation and stress concentration of any optical elements. As the large-aperture prism is characterized with non-uniform quality, rotating and titling motion, an adjustable segment-surface support way is proposed, and its specific program is designed. This paper analyzes the motion process under this support and gets the most dangerous condition. The optimization of the supporting angle under the condition is also made by the two-step optimization method, as a result, the maximum deformation peak-to-valley (PV) value and von Mises stress value in dynamic process have respectively decreased by 7.40% and 11.45% after optimization, which validates the feasibility and rationality of the optimized support way.