The invention discloses an air-cooling temperature-dropping and air-changing system for a transformer, which is applied to the air-changing in a generator transformer and a transformer chamber. The system is characterized in that relying on an original air duct and an original air inlet in the transformer chamber, cooling plates are arranged on a main transformer, an air blower is arranged under the cooling plates of the transformer, a lower flow guiding screen is arranged in the lower air duct of the air blower, airflow fences are arranged among the cooling plates of the transformer above the air blower, and an upper flow guiding screen is arranged beside the cooling plates of the generator transformer, and surrounds the cooling plates of the transformer in the shape of the letter C; and a temperature sensor is arranged on the transformer, a humidity sensor is arranged in the chamber, and the running and the stopping of the air blower are set by a temperature-humidity controller. On the basis of the characteristics, the temperature-dropping and air-changing system of the indoor transformer, which has that advantages of the natural and compulsory temperature-dropping and air-changing, simple structure, and good heat dissipation and air-exchanging, is manufactured. By adopting the scheme, when the generator transformer carries out temperature reduction and energy conservation, the damage to the generator transformer caused by high load and high temperature, and the loss to the users caused by the damage of the generator transformer are reduced.