Abstract: In order to do fine analysis on climatic characteristics of water vapor resource and its exploitation potential in Jiangsu Province, the EAR-Interim high resolution reanalysis data was applied to calculate the total amount of water vapor resource and its precipitation percentage, presentations of spatial distribution, seasonal variation characteristics, climate change trend and modes. The results showed that: the amount of water vapor resource (Q) in Jiangsu was 9223 mm in annual average and its precipitation percentage (P) was 11.4%. The resource (Q) exhibited a declining trend of 3 mm/a and had two typical anomaly patterns in the past 35 years. The first pattern was a high spatial consistency of anomalies, while the second pattern showed an anti-phase relation of variation in the northern and southern regions. Q and P exhibited the distribution of south more and north less. In North Huai River, Q and P was the lowest, and the trend of P declined in autumn and winter. Around Tai Hu Lake and the coastal region, Q and P both declined in spring, autumn and winter. In Ning-Zhen-Yang Region, the declining trends of Q and P appeared in spring and autumn. In spring, the declining trend of Q was the maximum with 4.4 mm/a, and the characteristic of south more and north less was the most significant with the maximum of 18%. In autumn, P was the minimum, only 8.4%. It is concluded that the exploitation potential of the water vapor resource in Jiangsu is tremendous. The intensity of the exploitation must be increased in spring and autumn, winter around the key region of North Huai River and summer around Tai Hu Lake and the coastal region.