Abstract: A control method for an open channel for obtaining a stable condition of flow of water by coping with a transient change therein, comprising the steps of representing each space divided by gates of the open channel by a three water tank model including three imaginary water tanks in series and two imaginary conduits connecting the imaginary water tanks with each other; solving this model so as to obtain estimated future values of parameters of a state of the open channel; and determining a degree of opening of each gate so as to keep a liquid level of the space constant on the basis of the estimated future values of the parameters.