Locking to the laser cavity length of ultra-stable cavities is an important method to gain ultra-short line width laser output. The stability of the laser relies on the length stability of the Fabry-Perot (F-P) cavities. Vibration induced cavity deformation is one of the dominate factors that affect the stability of ultra-stable optical cavities. The elastic deformation of two general cavities with different mounting configurations in vibration environment is quantitatively analyzed. Numerical results offer the optimum mounting configurations of the two cavities, where the change of vibration-induced cavity is minimized to 10-12 m