In Study on National Medium- and Long-Term Water Supply and Demand Planning, water demand and supply trend and existing problems in China since 1980 were analyzed. Water demand and supply trend schemes for 2000 and 2010 were proposed, and the scheme for the mid 21 century was analyzed. Feasible implementation scheme for water supply arrangement during the planning period was also proposed and the concept of “regional water supply capacity” was introduced for the first time, which laid a foundation for scientific utilization of water resources in the future.