The performance characteristics of isothermal fluidized bed syngas methanation for substitute natural gas are investigated over a self-made Ni-Mg/Al2O3 catalyst. Via atmospheric methanation in a laboratory fluidized bed reactor it was clarified that the CO conversion varied in 5% when changing the space velocity in 40-120 L.g(-1).h(-1) but the conversion increased obviously by raising the superficial gas velocity from 4 to 12.4 cm.s(-1). The temperature at 823 K is suitable for syngas methanation while obvious deposition of uneasy-oxidizing C. occurs on the catalyst at temperatures around 873 K. From a kinetic aspect, the lowest reaction temperature is suggested to be 750 K when the space velocity is 60 L.g(-1).h(-1). Raising the H-2/CO ratio of the syngas increased proportionally the CO conversion and CH4 selectivity, showing that at enough high H-2/CO ratios the active sites on the catalyst are sufficient for CO adsorption and in turn the reaction with H-2 for forming CH4. Introducing CO2 into the syngas feed suppresses the water gas shift and Boudouard reactions and thus increased H-2 consumption. The ratio of CO2/CO in syngas should be better below 0.52 because varying the ratio from 0.52 to 0.92 resulted in negligible increases in the H-2 conversion and CH4 selectivity but decreased the CH4 yield. Introducing steam into the feed gas affected little the CO conversion but decreased the selectivity to CH4. The tested Ni-Mg/Al2O3 catalyst manifested good stability in structure and activity even in syngas containing water vapor. (C) 2014 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.