Structural stability of vacuum chamber assembly significantly affects alignment precision of laser beam and target in Inertial Confinement Fusion(ICF) facility. Structural stability optimization for vacuum chamber assembly is processed in this paper. Dynamic performance of vacuum chamber assembly was first studied. Natural frequencies and vibration modes were analyzed. Then influences of supporting frusta structural parameters on natural frequencies were investigated. And the model of influence was established. Last, the optimization of the supporting frusta structural parameters was carried out and the first natural frequency was improved to 14.44 Hz that satisfied the stability requirement of the ICF facility.