Urban and rural atmospheric humidity differences were analysed and studied based on the hourly average data collected in two representative meteorology stations (TKL, 15m, 22°31’43 “N, 114°09’24 “E and HKO, 32m, 22°18’07 “N, 114°10’27 “E) in Hong Kong during the period of 1994 to 2009. It was found that in winter season (December and January), the urban areas were more humid than rural areas with the highest UME value of 2.28hPa while thus phenomenon was rarely significant in the summer season which is coordinate with UHI phenomenon. In addition, an urban moisture balance model, based on urban surface hydrology and urban atmospheric moisture balance, was developed to assess the different factors on the temporal behaviour of urban moisture environment. The performance of the urban moisture balance model was also discussed. We conclude that the impact of precipitation on urban moisture environment is important for the high-compact and high-rise city with limited vegetation ratio. Moreover, urban moisture environment is affected by urban morphology, anthropogenic moisture and weather conditions.