After estimating the potential resource of rainwater in Wangwa watershed in Pengyang County, the relationship between its potential and supply was appraised based on the development programmer of water saving agriculture and actuality of land use and rainwater data in the watershed. The results showed that: (1) the potential of theoretical resources of rainwater was 7682598 m³, the ratio of using in the same spot , different spot and rainwater collection reiterative utilization is 50.96%, 7.16% and 41.88% respectively. (2) Potential of realistic rainwater was 7164885 m³, which was 93.26% of the potential of theoretical resources. (3) the demand of water in demonstration area was 3 739 352m³, just was 52.19% of the potential of theoretical resources, the remain of Potential of realistic rainwater could be used. (4) the result on assessment of rainwater using in the watershed suggested that the scales of rainwater using was insufficient, so it should be a efficient approach of rainwater resources to enlarge the scales of rainwater using in the same spot.