Numerical analysis of O3 depletions by exhaust plume from stratospheric flight at the altitude of 25km was conducted. Expanding box method was employed to simulate a diffusion of exhaust plume in the stratosphere. Concentrations of chemical species and normarized sensitivities of O3 concentration for reactions were estimated by fifth-order BDF method. Chemical kinetics include NOx, HOx and Ox chemistry. As results, it takes over two days that O3 concentration within a plume becomes ambient lebel within 1ppb. O3 perturbations were changed by an effect of plume-emission time, and they are bigger in daytime than in nighttime. Distributions of sensitivities of O3 concentrations for reactions are also changed for the plume-emission time. O3 depletion is greater by NOx than by HOx in exhaust plume.