The invention discloses a device and a method for adjusting the flame temperature of VAD and OVD on line. The device comprises a blow lamp and a sleeve arranged at the outlet of the blow lamp, wherein a heating device I sleeves the outer surface of the blow lamp; a heating device II sleeves the outer surface of the sleeve; a part, close to the outlet of the blow lamp, of the prefabricated rod loose body is adopted as a deposition area of the prefabricated rod loose body; a pair of heating devices III are arranged close to the deposition area; and the heating devices III are arranged in front of and behind the deposition area. By adopting the device and the method disclosed by the invention, the stability of refractive index profile distribution of an optical fiber prefabricated rod is improved. As the refractive index profile distribution of the optical fiber prefabricated rod and the stability of the refractive index profile distribution can be affected by the flame temperature and the temperature of the deposition area, the temperatures of the flame and the deposition area are controlled by using an external heating body (a graphite resistor or a resistance wire), the temperature control precision and the stability are both good when being compared with pure combustion flame, and the result shows that the refractive index profile distribution of the optical fiber prefabricated rod can be relatively precise and stable.