The utility model discloses a self-adjusting lubricating structure of a fan bearing. The self-adjusting lubricating structure comprises a fan main shaft, a bearing fixed on the fan main shaft, a bearing box, an impeller, a lubricating oil tank arranged below the impeller, an oil supply pipe, an oil return pipe and an impeller cover, the fan spindle penetrates through the bearing box, the bearing is located in the bearing box and fixedly connected with the bearing box, the impeller is sleeved on the fan spindle outside the bearing box, and the lower portion of the impeller is soaked in the lubricating oil tank. The fan has the advantages that the impeller and the fan are started and stopped at the same time, it can be guaranteed that lubricating oil enters the bearing box to lubricate the bearing as long as the fan rotates, and continuous and normal operation of the fan is guaranteed; the function of automatically adjusting the lubricating oil amount can be achieved, the safety coefficient is improved, bearing abrasion and ablation are greatly reduced, the service life of the bearing is greatly prolonged, and the operation safety of the draught fan is improved; the structure is simple, an oil pump does not need to be additionally arranged, and economic cost is reduced.