In SHENGUANGII (SGII) facility, the optomechanical system is the optics and optomechanical support hardware which necessary to transport the laser beams through the system from the laser drivers to the target. In order to satisfy the laser beam accurately positioned, the system must provide a stable platform for the optical elements before and during a shot. While the ambient vibration such as thermal impact, ground borne, acoustic and noise usually disturbs the stability of the system when the facility on working. This paper put forward the concept of system stability, and the method of test and vibration isolation control presented. The finite element analysis has been used to analysis the stability of the typical system. Base on the result, the working performance of system can be confirm, even the stability of SGII facility in future long-time work can be estimated, also the key points of stability design for the important parts and system can be suggested. It offers design guidance on the next upgrade of SG facility design and guarantee for the procedure of facility's precision. This information also can be used to the structure and system of the similar facilities.