A gas concentration detecting device consisting of catalytic burning sensors and an on-line computer data collecting system was set up to investigate axial and radial mixing characteristics of gas in adsorptive bed. The principles of the device were also introduced in some detail. It could measure and record combustible gas concentration at sixteen positions simultaneously in an adsorptive bed. Experiments were carried out with methane-air-5 Angstrom molecular sieve in a 267 mm ID adsorption column at different gas flow rates. Methane used as adsorbate was continuously fed into the center of the bed entrance section and its concentration distributions were obtained at three levels of the column. This device can also be used to measure temperature distribution if temperature sensors are used instead of that for gas concentration measurement.