Frequency-tripled Nd∶YAG laser was used to pre-treat optical film samples. The capacity of optical film′s resisting laser induced damage is affected by laser preconditioning, but the influence regulations are very complicated. Results reflect that appropriate pre-treating laser energy density is related to testing laser energy density. From the aspects of laser annealing and laser induced slight damage in pre-conditioning, the probability statistical model of laser-induced damage deduced by the author can explain these complicated phenomena well. Generally, if the energy density of preconditioning laser pulse is below the critical energy density for laser annealing, the effect of laser precondition is negative mostly; when the energy density of preconditioning laser pulse is beyond the critical energy density for laser anneal and below that for laser induced micro-damage, the effect of laser precondition is positive mainly. It is appropriate to choose the preconditioning pulse energy density in this scope; while if the energy density of preconditioning laser pulse is beyond the critical energy density for laser induced micro-damage, the effect of laser precondition is negative mainly.