The invention provides a detection method for the air-tightness of a flexible packaging product and a flexible packaging battery; the flexible packaging product or battery is placed in a closed container and filled with detection gas, the product or battery to be detected is placed in the other closed container and vacuumized, the air-tightness of the flexible packaging product or battery to be detected can be determined by a detection device, and therefore this kind of method can implement the high-precision detection for the air-tightness of the flexible packaging product or battery; even though the flexible packaging product or battery has the slight air leakage, to select the appropriate detection gas and the sensitive detection device can implement the accurate detection for the air-tightness of the flexible packaging product or battery.