In this paper for methanol synthesis from the hydrogenation of CO and CO2 over surface poisoned or unpoisoned Cu-based catalyst, three kinds of diffusion models for calculating the intraparticle effectiveness factors of the multiple reactions have been presented. They are one dimensional multi-components diffusion model, one demensional simplified multi-components diffusion model and one dimensional key-components diffusion model. Numerical solution of the intraparticle effectiveness factors solved by orthogonal collocation method have been obtained. Key-components diffusion model was available for calculating effectiveness factors only for the reactions over slightly poisoned catalyst. As poisoned fraction increases the deviation of effectiveness-factors calculated from key-components diffusion model and multi-components diffusion model gets greater. Since the time spent for calculating simplified multi-components diffusion model is less and the results are more precisely, this model is recommanded for calculating effectiveness factors.