Abstract: Based on the differences of relative humidity between urban weather stations and suburb weather stations as the intensity index of dry and moisture islands, air humidity changes and its responses to the urbanization from 1964 to 2007 in Chengde were analyzed by the trend analysis method and other statistical methods. The results show that air humidity has an obvious increasing trend in the recent 44 years in Chengde, especially in the last 10 years. Furthermore, air humidity characteristics turns from dry island to moisture island since 1988. Moisture island effect is obvious in both summer and autumn. The significant changes of humidity field are mainly caused by the urbanization.