Abstract: Boersma-Klein and Moulijn evaluated the transport coefficients of non-adsorption system by a new method-the improved curve fitting domain. in time which combines Fourier analysis with the traditional curve fitting in time domain, and substitutes the error map plotting with a set of computer program of linear and non-linear regression. In this paper, the calculations of Fourier analysis and the curve fitting in time domain are based on the simplex method of polydimensional search technique, which means the simplification of the work of Boersma-Klein et al. Moreover, the application of the improved curve fitting in time domain is extended to adsorption system, and five transport and adsorption coefficients of domestic C301 methanol synthesis catalyst in fixed-bed reactors are obtained. The advantages of this method and the selection of harmonic number and period for its use are also discussed.