Small Scale Hydroelectric Power Generation is made using the Water drop caused by the gradient difference between that of the river and that of the water guide channel. The water flow in this system apt to vary with time. Especially, at the time of the flood or that of the dry, the flow in the water stream varies largely. To realize the stable generation, it is necessary to maintain the water level of the head tank located in the mid way of the stream channel at a constant level. In this paper, variation of water level is forecasted using two tank models for the water channel and head tank and the water level control algorithm is proposed by finite settling time control. The effectiveness of the algorithm is evaluated beforehand using the simulation program of the water environment for the hydroelectric generation system.