The main purpose of this study is to detect the integrity of welding steel plate by using ultrasonic testing .The results of this investigation show that it is quite difference between the completely welding steel plates and the defectively welding steel plates. The reflective amplitude of completely welding steel plate is low and uniform whereas it is high near the welding place to the defectively welding steel plate. Thus, it is a powerful and useful tool to detect the welding steel plate by means of ultrasonic technique.