In SNG (synthetic natural gas) process by proposed RIST(Research Institute of Industrial Science & Technology)-IAE(Institute for Advanced Engineering) (including three adiabatic reactors and one isothermal reactor), the methanation reaction and water gas shift (WGS) reaction take place simultaneously, and the supply of steam with syngas might control the temperature in catalyst bed and deactivate the catalyst. In this study for development of SNG process, the characteristics of the methanation reaction with a Ni-based catalyst by prepared RIST and using a low H2/CO mole ratio (including CO2 22%) are evaluated. The operating conditions (H2O/CO ratio of the 1st adiabatic reactor, operating temperature range of 4th isothermal reactor, etc.) were reflected the results from previous studies and in the same condition a pilot scale SNG process is carried out. As a results, the pilot scale SNG process is stable and the CO conversion and CH4 selectivity are 100% and 96.9%, respectively, while the maximum CH4 productivity is 660 ml/gcat·h.