The invention relates to an outdoor warning board convenient to clean. The outdoor warning board convenient to clean comprises a cross rod, a vertical flat plate and supporting legs arranged at the lower end of the flat plate, a warning sign setting region and a transparent protection plate covering the warning sign setting region are arranged on the front side surface of the flat plate, brush bristles which are used for cleaning the transparent protection plate are arranged on the cross rod, sliding grooves which extend in the up-down direction are formed in the left end and the right end ofthe flat plate, sliding blocks are connected in the sliding grooves in a sliding mode, the sliding blocks are connected with the cross rod together, a rubber inflatable jacking rod with the upper endwhich is connected with the sliding blocks together and a rubber inflatable downward push rod with the lower end which is connected together with the sliding blocks are arranged in the sliding grooves, the lower end of the rubber inflatable jacking rod is connected together with a first air outlet of a three-way valve, and the upper end of the rubber inflatable downward push rod is connected witha second air outlet of the three-way valve. According to the outdoor warning board convenient to clean, a solar street lamp with a warning sign which is not prone to damage and the flat plate which isconvenient to clean is provided, and the problem that a warning sign of an existing warning board is prone to damage and inconvenient to clean is solved.