Abstract: Experimental investigations on combustion oscillation in boiler furnace were performed. The results showed that pulsating oscillation intensity of smoke in boiler furnace was in proportion to environmental disturbances, such as unstable blower airflow and variety of fuel-air ratio. Oscillation frequency of smoke was mainly less than 10 Hz, belonging to low frequency range. The experiments also showed that combustion oscillation would occur when the measured Re numbers went beyond a specific Re number. A criterion explaining combustion stability （critical Re）, was presented, and the expression of critical Re was also given. Improving critical Re numbers will enhance combustion stability, and so eliminate or weaken combustion oscillation. This paper can be useful in improving boiler furnace design.