The laser-induced damage threshold (LIDT) of optical films is an important index for assessing the film′s properties of laser tolerance. Accurate measurement for the LIDT is the foundation of laser tolerance estimation and data comparison of the thin films. Based on the analysis and computer simulation, the optimization ways of laser-induced damage threshold was presented in this paper. The results show that the error of the energy density increased with the increase of the laser energy at a fixed laser spot. Therefore, in the case of satisfying the need, it is better to choose low laser energy for the testing system. Under the fixed laser energy, there will be a critical laser spot. The error of the energy density changed strongly with the spot size change: smaller spot size, bigger energy density error. The small gentle energy density error can be obtained at the laser spot size greater than the critical laser spot, vice versa. Therefore, it is better to choose the spot size equal or greater than the critical laser spot size. The fitting maximum error is equal to that of the error of the maximum laser energy level. Thus it can be seen that the uncertainty of a LIDT test system can be reduced through designing suitable laser parameters.