Abstract: A simplified optimal operation model for multiple reservoir system,dynamic emptying storage coefficient method,is introduced by least surplus water in this paper.The emptying storage coefficient of a reservoir at any time indicates the ability of water storage and supply of the reservoir at that time.Based on this method,the storage and draft orders of a multi-reservoir system are determined by the factors of every reservoir of the system in the initial of a time interval,and the emptying storage coefficients of every reservoir are kept equal at the end of the interval under constraints.In this way,the runoff can be retained in reservoirs as much as possible and waste water will be minimized.The model is simple and easy,and can be used for small multiple reservoir system with multi-purpose.