An air filter leak inspection method is provided. First, an aerosol to be filtered containing particles is passed through an air filter having a first edge and a second edge. Next, a leakage inspection unit is provided. The leakage inspection unit includes n probes, wherein n indicates a positive integer. Afterward, a moving procedure is set to make the probes traverse between the first edge and the second edge, thereby scanning the whole portions of the air filter. When the probes move to the second edge, the probes move along the extending direction of the second edge with a designed distance, wherein the designed distance is less than the length of each probe. Besides, the number of times that the probes traversing between the first and the second edge is determined according to the amount of the probe, the length of each probe and the height of the air filter.