The invention relates to a method of gas leakage detection for a dry air-insulated composite apparatus. The composite apparatus adopts a dry gas to replace an SF6 gas in an insulated mode; an inert gas with a volume ratio of 0.5% to 1.5% is injected to the dry air to form the dry gas; and the leakage positioning problem of the dry air-insulated composite apparatus can be realized by using the existing infrared imaging leakage detection technology. When the method of the invention is applied, the cost can be reduced, the investment can be reduced, the leakage positioning problem of the dry air-insulated composite apparatus can be realized by using the existing infrared leakage detection technology, the operation is conventional and simple, the observation is convenient, and the promotion value and the application value are extremely high.