The invention provides a twin-tooth radiating fin, an outdoor cabinet adopting the radiating fin as cooling device and a cooling method thereof. The twin-tooth radiating fin comprises a blade connecting piece, a first and a second blade groups which are connected with the blade connecting piece and arranged on two sides thereof. The outdoor cabinet includes a sealing cabinet body, an internal circulation air passage is formed between the inside of the sealing cabinet body and a baffler in the cabinet, a heat generating device is arranged in the internal circulation air passage, a twin-tooth radiating fin is arranged on the sealing cabinet body, the first blade group thereof is arranged outside of the sealing cabinet body, the second blade group is arranged in the internal circulation air passage, the internal circulation air passage is provided with a blower fan. After working, the blower fan in the internal circulation air passage is started, heat generated by the heat generating device is carried to the internal circulation air passage by airflow, transmitted to outside of the sealing cabinet body through the twin-tooth radiating fin, then dispersed to external environment. By utilizing the new twin-tooth radiating fin structure, the outdoor cabinet can satisfy protecting and cooling requirements without using air conditioners and heat exchangers.