Abstract: Coated steel was used as car body materials to prolong the life of car. However, it is difficult to be welded, and the reliability of ultrasonic testing(UT) technology is not good for sheet steel spot-welded joint. So far no suitable nondestructive testing method can be used to inspect the quality of coated-steel spot-welded joint exactly. A method which combined the UT technology with digital signal processing technology was studied. The results showed that the method could improve the reliability of inspection for car body coated steel spot-welded joint.