A thermal fracture process applied to the brittle materials has become a foremost technology, and applied to cut the LCD glass substrate. One advantage of this process is that the cross-section of cut glass substrate will be smooth with low residual stress after thermal fracture processing. The multi-sphere mirror aims to repeatedly reflect the light energy within upper and lower mirror in order to enhance the laser beam absorption rate of glass under cutting. Moreover, with a proper design of multi-sphere mirror, the energy distribution of applied laser can provide an ideal thermal fracture condition to improve cutting speed of glass substrate. A novel reflective mirror with multi-sphere surface was developed and reported to transform the regular laser energy distribution toward the ideal one. Furthermore, the shape of multi-sphere mirror is optimized by Taguchi method so as to meet the surface requirement that can get the ideal energy distribution. This paper presents a series of simulation results and analysis results of multi-sphere mirror calculated by the TracePro opto-mechanical software.