Experiments were performed to investigate the influence of humidity on a doubleswirlded nonpremixed syngas burner. Planar laserinduced fluorescence (PLIF) of OH radical measurement was adopted to identify main reaction zones and burnt gas regions as well. Together with the temperature and emission measurements during the exhaust section, some important characteristics of the syngas flame were investigated in detail. The results indicate that fluorescent signal strength of OH radicals pronounce weakening, and the flame gradually show a W type distribution with the increase of humidification amount. CO missions in combustor change little when φ is in the range of 0 to 30%, but increase quickly when φ is over 40%. NOx missions in combustor reduce continuously with the humidity of air increaseing. However, the slope of NOx descending decreases when φ is over 20%.