The invention discloses a heat dissipation mechanism for a gearbox of a wind driven generator. A horizontal partition plate is fixedly arranged in an outer case, a water-cooling heat dissipation mechanism is installed at the upper end of the partition plate, a heat dissipation pipe is connected with the water-cooling heat dissipation mechanism, and the heat dissipation pipe extends downwards to the position below the partition plate; and the gear box is located in the middle of the lower end of the outer case, connecting frames are fixedly connected with the lower end of the partition plate, the two connecting frames are located on the two sides of the gear box correspondingly, and the connecting frames are parallel to the side wall, provided with a heat dissipation opening, of the outer case. According to the heat dissipation mechanism, two heat dissipation fans drive air around the gear box to distribution rapidly, low-temperature air dissipates heat of the gear box, the heat dissipation effect on the gear box is improved through air cooling circulation, meanwhile, circulated distribution cooling water in a water cooling heat dissipation mechanism conducts the heat of the gear box, and air cooling and water cooling are carried out synchronously, so that the heat dissipation efficiency and the heat dissipation effect of the gear box are ensured.