The invention discloses a modeling method of a water turbine and a regulating system thereof. The modeling method is applied to the island model of the water turbine and the regulating system thereof. The modeling method comprises the steps of setting up an actuating mechanism model with a variable time constant method based on opening hysteresis so as to achieve simulation of the segmental closing characteristic of the actuating mechanism, and setting up a water turbine model with a piecewise function so as to achieve simulation of opening and power non-linear characteristic of the water turbine at the full-load segment. The models set up by the modeling method are simple and clear, and a speed governor model, the actuating mechanism model and the water turbine model are more practical, not only the quick and non-error adjustment of the frequency of an island power system can be achieved, but also the opening and power curve non-linear simulation of the water turbine at the full-load segment can be achieved; the simulation result is closer to the actual curve.