Abstract: The Double-layer Heterogeneous Conductor (DHC) such as the lap-joint copper-aluminum transition terminal clamp is widely used in pivotal engineering fields including energy, aerospace, etc. The unstable welding control conditions would leave the welding interface vulnerable to interface damages such as the wall-thinning defect in the conductive layer, it is imperative to detect and evaluate welding-interface damages with effective nondestructive evaluation techniques. In this paper Transient Eddy Current (TEC) inspection of the wall-thinning defect occurring at the welding interface of a lap-joint copper-aluminum transition terminal clamp was intensively investigated. The characteristics of the TEC response to the interface damage were scrutinized via finite element analysis. A TEC signal feature and assessment method for evaluation of the wall-thinning defect were proposed. In parallel, an experimental platform of TEC inspection of DHC was built up for further investigation regarding imaging and evaluation of the wall-thinning defect at the welding interface. From the results of simulations and experiments, it was found that the proposed TEC signal feature and evaluation method were capable of quantitatively evaluating the interface damage of the lap-joint copper-aluminum transition terminal clamp.