Abstract: According to measure and data, the author shows main features of rivers in the Sanjiang Plain and change of water balance on time and space, and then estimates water resources of five types, i.e.runoff, underground water, soil water, supplied water from the three rivers and lake (or reservior) water. Sum of the five water resources can be up to 32.3 billion m³. But they are rather unwell-distributed, the annual range is rather considerable too. Up to now, only 7.7% of water resources have been utilized, according to programme, 17.8 billion m³ will be utilized in furture in the area. Rationally exploiting water resources in the area should combine with protection and management, and the criterion judging rationality of utilization only is beneficial results on economic, ecologic and social aspects. During exploitation and utilization, it is important to provent water resources from pollution.