Abstract: The irregular A301 ammonia synthesis catalyst is spheroidized by means of shape factor and equivalent diameter. The tortuosity factor of irregular A301 catalyst is determined by single pellet string reactor method (SPSRM). So a one - dimensional isothermal multi- component diffusion ?reaction model is established in the irregular A301 ammonia synthesis catalyst based on the intrinsic kinetics under high pressure. The orthogonal collocation method as well as Broyden method was used to solve the model equations. The intraparticle diffusion efficiency factor and the concentration distributions of individual components in the catalyst are obtained. The model is verified by the global kinetics data under high pressure obtained in a gradientless reactor. The calculation data agree well with experimental data, so the spheroidized model can be used to describe the diffusion- reaction process in the irregular catalyst and to calculate the intraparticle diffusion efficiency for engineering design.