Abstract: The battery pack of new energy vehicles adopts a large number of wire bundle-electrode welding structures. Based on the material composition and structural characteristics of this structure, the suitability of the conventional water-immersion coupled ultrasonic reflection method for testing the welding quality between the wire bundle and the electrode was analyzed. It was found that the coupling method and longitudinal resolution of the conventional approach were unable to meet the testing requirements. A water-film coupled, high-resolution ultrasonic C-scan reflection testing method based on multiple echo amplitude integration was proposed. The results show that the proposed testing method can detect all artificial welding defects with a diameter of 0.5 mm or larger in the aluminum electrode/copper wire bundle welding sample; it can also detect unwelded defects in actual products, and the ultrasonic testing results accurately correspond to the fracture surface analysis.