To discuss the impact of the quantificated identifying index on fog and haze observation, some comparisons are conducted on fog days, mist days and haze days from 18 stations in Hubei Province from 2006 to 2012 One dataset is used as the initial records without quantificating, while the others are processed with the quantificated identifying index. The results shows that by the quantificated identifying index, the number of haze days increases obviously, while the numbers of mist and fog days moderately decrease. As for Hubei Province, there would appear fogs or light fogs when relative humidity between 80% and 94%. By the statistical analysis of hourly record humidity, visibility, and weather patterns, the homogeneous dataset of fog, mist, and haze can be obtained to realize the modification of the historical records. Nevertheless, observers should not use the quantificated identifying index only; weather situation must be well considered to avoid frequent shifts between mist and haze while mist developing, mist disappearing, as well as the value being around the critical levels.