Optical mounts structure stability is crucial to beam position accuracy. The study on optical testing method for structure stability of mirror /lens mounts was involved and optical stability testing software was compiled. Structure stability of different kinds of mirror /lens mounts was measured. The variation of beam position drift versus time was experimentally obtained, and the comparison of stability properties among different kinds of mounts and different levels of adjustment were made. Stability test system was able to gives on accuracy of as high as 3.13 μm. A rapid and handy testing mean for stability of optical mounts was provided, and the results can be used as a key guide to optical mounts choice for high power excimer laser system.