The exponential fitting model of damage probability and 1-on-1 laser damage threshold of optical components was presented, and the effects of irradiated spot size and number of spots tested for one pulse energy density on damage probability were investigated. The damage probability was calculated, when the defects is distributed as complete degeneracy, and then further modification was done to fit the incomplete degeneracy situation. The damage probability to fit the damage data is called exponential fitting model and the experiment results in the paper showed that the exponential fitting could get more accurate damage threshold. The test errors induced by laser beam spot and the sites tested at one pulse energy density were studied through numerical simulation. It is shown that the larger beam area and more sites exposed at one pulse energy density, the more accuracy of damage possibility.