The invention relates to a windproof mechanism for the outdoor advertising board, which comprises a mounting box, two bearing seats are fixed to the top of one side of the mounting box, a first rotating shaft is rotatably mounted on the axes of the two bearing seats, and swing plates are fixed to the outer walls, close to the two ends, of the first rotating shaft; rotating shafts are rotationally installed on the opposite faces, close to the tops, of the two swing plates, rotating rollers are rotationally installed on the outer walls of the rotating shafts and the first rotating shaft in a one-way mode, and an advertising tape is jointly installed on the outer walls of the two rotating rollers in a transmission mode, a deflection mechanism for driving the two swing plates to deflect are also included, the deflection mechanism comprises two first sliding grooves, and the two first sliding grooves are formed in the top, close to the two swing plates, of the mounting box correspondingly. Through cooperation of the structures, the effect of lodging the advertising tape in advance is achieved, the situation that the advertising tape is blown off by wind due to the fact that the area of the advertising tape is too large is prevented, and therefore the windproof effect of the advertising tape is improved.