Abstract: The equilibrium substance composition of ethanol steam reforming system was calculated by thermodynamics and compared with measured ones.Effects of temperature,pressure and water/ethanol molar ratio were also analyzed with thermodynamics theroy.The results show that the decrease of pre-(ssure) favore the steam reforming of ethanol in this system.The conversion of ethanol and the content of(hydrogen) increase with the increasing of reaction temperature,when water/ethanol molar ratio is equal(to 8 at) 101.325 kPa.At 900 K the higher water/ethanol molar ratio the desired reaction of ethanol steam(reforming) become predominant one.The calculated trendlines of composition are in accordance with the(experiment) ones,which further proved the correctness of the thermodynamic analysis.