External noise will affect the results of Lamb wave damage imaging. To solve this problem, a damage factor based on EMDHilbert transform is defined. First, air-coupled ultrasound is used to excite-receive A0 mode Lamb waves in the aluminum plate, and scan them in two orthogonal directions to obtain the received signal. Then, the signal is decomposed by EMD to find the IMF component with the greatest correlation with the original signal. The Hilbert transform is performed to obtain the envelope curve, and the relative change of the envelope curve area is defined as the damage factor. Finally, white noise with different signal-to-noise ratios is added to the scan signal to simulate the noise environment, and damage imaging is performed before and after the simulated noise environment. The results show that the proposed damage factor can effectively form image of the damage in the aluminum plate, and has certain noise resistance. Compared with the imaging result without adding noise signal, the maximum error change is 0. 8 mm.