The invention discloses an automatic line changing device for a photovoltaic panel cleaning machine. A track is arranged in the direction of a perpendicular line between every two adjacent photovoltaic panels and located on the outer side of one end of each photovoltaic panel. The shape of a line changing support is matched with that of the side face of each photovoltaic panel. Rolling wheels are rotationally arranged at the lower end of the line changing support, connected with a rolling wheel driving motor and driven by the rolling wheel driving motor. A lithium battery is fixed to the line changing support to supply power to the rolling wheel driving motor. Two sliding rails are horizontally arranged and fixed to the upper side and the lower side of the line changing support respectively. The two sliding rails correspond to sliding rails on the photovoltaic panels in position, and when the line changing support slides to the side faces of the ends of the photovoltaic panels, the sliding rails on the line changing support are in butt coincident fit with the sliding rails of the photovoltaic panels. According to the automatic line changing device, the structure is simple, operation is convenient, continuous cleaning of the multiple rows of photovoltaic panels is achieved, and the photovoltaic panel cleaning efficiency is greatly improved.