This paper studies the heat and mass transfer characteristics in a steam reforming reactor using numerical simulation and investigates the operating parameters for effective hydrogen production. Simultaneous analysis of governing equations and chemical reaction equations is carried out in a multiphysical simulation. The major reactions are assumed to be the steam reforming, water-gas shift (WGS), and direct steam reforming reactions. The temperature and species concentrations measured for the experiment are compared with numerical results. After validation of the developed code, numerical work is carried out to study correlations between the performance and operating parameters, which are the wall temperature, the inlet temperature, the steam to carbon ratio (SCR), and the gas hourly space velocity (GHSV). The fuel conversion increases with the high wall temperature due to the increased heat transfer. The inlet temperature may not affect the fuel conversion, if the reformer length is long enough. However, the heat transfer limitation can occur near the inlet when the inlet temperature is over 300 °C. The concentration of carbon monoxide becomes lower with increasing SCR due to the decreased WGS reaction rate. The high GHSV causes the short residence time and it is the reason for the low fuel conversion.