The invention relates to a simple closed opening type water wave generator which comprises a generating set (1) connected to an electric power transmission device, and a closed opening part (2), wherein the generating set comprises a generator body (11), the input shaft of which is connected to a blade shaft (14) with a blade (13) through a coupling (12); the closed opening part comprises a closedopening (21) for importing a water wave and transferring the water wave; a water inlet facing the water wave is formed in one end of the closed opening while the other end of the closed opening integrally communicates to one end of a straight opening (23), the blade shaft with the blade is arranged at the outlet of the other end of the straight opening, the inner part of the straight opening is hollow, and the closed opening and the straight opening are separately supported by means of supporting columns (22) fixedly arranged in the water wave. The simple closed opening type water wave generator provided by the invention can not only collect a lot of sea water waves to generate electricity but also collect small waves of other water surfaces to generate electricity.