Abstract: The steam gasification experiments with Neimeng lignite, Shenfu bituminous coal, Zunyi anthracite and a petroleum coke were conducted in a thermogravimetric analyzer (TGA) to study the intrinsic kinetics and the macrokinetics with the effects of particle size. By virtue of gas-solid catalysis theory, a method to calculate the internal effective factor was proposed based on the kinetic parameters derived from the nth-order equation. The comparison between calculated and experimental effective factors shows that the method is better to calculate the internal effective factor for quantificationally estimating the effect of internal diffusion on steam gasifiation.