The invention relates to the technical field of high voltage equipment and gas insulating materials and particularly relates to a fast mixing device of SF6 and N2 gases and a gas filling method. The fast mixing device comprises a protection shell, wherein a connecting element is arranged at each of the two ends of the protection shell; a blocking groove and a bracket are fixedly arranged on the inner wall of the protection shell; a rotating element is arranged on the bracket; one end of the protection shell is connected with a mixed gas filling gas path system; the other end of the protection shell is connected with gas insulating equipment. The fast mixing device is directly mounted on the mixed gas filling gas path system, and the structure and the function of the mixed gas filling gas path system are not changed, so that the fast mixing device is safer and more reliable; the fast mixing device has the characteristics of conciseness, flexibility and practicability; mixed gas is filled by utilizing the device, so that direct testing or application can be realized under a condition that the gas insulating equipment does not need standing, therefore, the device has comparatively high practical engineering value.