Abstract: In order to study the impact of urbanization on the Jining relative humidity, based on the relative humidity data collected from 1981 to 2010 of Jining City and its surrounding counties, including Yanzhou City, Wenshang County and Jiaxiang County, the author analyzed the variation tendency and characteristics of relative humidity of both the suburb and urban areas of Jining City. On the basis of this, the author investigated the influence of city development to relative humidity. The results showed that: (1) relative humidity of both suburb and urban areas of Jining City tended to reduce annually with similar feature. The largest reduction of relative humidity appeared in spring and autumn and reduction speed in suburb was higher than that in urban area, which meant suburb and urban areas of Jining City was now becoming warmer and drier. (2) Annual average relative humidity of Jining City in recent 30 years reflected typical dry island phenomenon and had upward trend, which was especially obvious in the 1990s. Although dry island phenomenon after the year 2000 was still higher than average, it decreased substantially. (3) Dry island phenomenon of Jining City beared distinctive features with different month and season: the second half of year was higher than the first half and it had the tendency to be stronger in all four seasons, strongest in spring and autumn, weakest in summer, while average in winter. Dry island phenomenon change in seasons went with change of years, strongest from 1991- 2000 and decreased after the year 2000. It was found: dry island phenomenon from yearly data on average at the time of 2:00, 8:00, 14:00 and 20:00, with its strongest at 2:00 and weakest at 14:00.