Abstract: Rational development and utilization of water resources is a key to alleviate the contradiction between supply and demand of water resources. In plain areas, the water sources interlace, so the incoming water and local water cannot be calculated separately. Therefore, it is of great value to propose a calculation method of water resource availability in the region. Taking Lixiahe area, a typical plain river network of Jiangsu Province, as an example, this paper constructed a generalized reservoir regulation and storage model in plain area to calculate the water resource availability under 24 scenarios (different engineering water intake capacities, inflow frequencies, ecological water levels). The results showed that under the current, planned and future project water intake capacities, the water resource availability in the Lixiahe area was in the range of 8.101 billion ~9.799 billion m3, 9.573 billion ~10.490 billion m3 and 9.380 billion~11.441 billion m3, respectively, which were positively correlated with the inflow water and the project water intake capacity, but decreased with the increase of ecological water level. Based on the calculation results, in order to alleviate the shortage of water resources in the study area, it is suggested authority take measures such as construction of the water pumping projects and the optimization of the water supply pipe network. The research results have practical and reference value.