The authors have developed a catalytic combustor for a CO2 generator that does not exhaust harmful emissions even though it’s a low-temperature(<990℃) combustion. However, the catalytic combustor has some problems of combustion instability depending on the surrounding environments (temperature, humidity) and/or taking a long time to ignite. In this study, the improvement of ignition delay and combustion instability of the catalytic combustor were studied. Ignition did not occur in a high humidity environment with a relative humidity of 80% or more, and a longer preheating time was required in 15℃ environmental condition. To solve the problem, we devised a method by adding a small amount of ethanol during the preheating period at specified catalyst temperature conditions. It was possible to stably ignite the catalyst even in a high humidity environment. The ignition time was able to shorten the preheating time by up to 55% regardless of the influence of ambient temperature and humidity. The optimum ethanol supply condition is to inject a total amount of 20 cc at a injection rate of about 0.8 cc/sec when the range of catalyst temperature is 200 to 220℃.