The invention discloses a method for expelling fouling organisms on a small ship to by using a washing device. A vertical rotary washing device is suspended at the edge of the upper side of a ship side by using a lifting rope and is adsorbed to the external side of a hull at a first height by means of a magnetic attraction force; the rotary washing device is started to begin to clear the fouling organisms on the external side of the hull; the upper end of the lifting rope moves along the edge of the upper side of the ship side at a constant speed; the rotary washing device synchronously and transversely move in a direction consistent with the direction of the upper end of the lifting rope along the external side of the hull under the action of a counter-acting force of the hull so as to finish the clearing of the fouling organisms at the first height; the lifting rope is enabled to form an included angle of 20-30 degrees with the vertical direction; the rotation axis of a washing partof the rotary washing device is inclined; the rotary washing device moves to a second height on the external side of the hull in a downwardly inclined manner; and the clearing of the fouling organismson the external side of the hull can be finished in sequence by repeating the steps. According to the method for expelling the fouling organisms on the small ship to by using the washing device, thefouling organism clearing cost is low, the fouling organism clearing effect is good, and the problems of high requirements on personnel and potential safety hazards can be solved.