Abstract: The feasibility of eddy current testing(ECT) technique in the nondestructive testing(NDT) of ultralight lattice material was studied. Numerical models were proposed for two kinds of ultralight sandwich plates of ripple and truss inner layer. The ECT signals from the cracks in the welding zone and from the welding joints in the sandwich plate were simulated and their features are compared based on the proposed models and by using an FEMBEM hybrid code. The effects of the random variation in the shape of welding bead on the ECT signals, the efficiency of the multifrequency algorithm(MFA) for the crack signal extraction were also investigated. The numerical results showed that the phase property of the welding noise and the crack signals were significantly different. The phase of crack signal was more sensitive to the excitation frequency. The crack signal polluted by the welding noise could be extracted by using the multifrequency signal processing algorithm. All the results showed that ECT was a promising option for NDT of sandwich lattice metallic plate.