Abstract: This paper introduces the practical experience of ultrasonic testing about T-Shape Welded Joints, the geometrical and welding characteristics are: the web and wing plates is of unequal thickness of less than 25mm,and the web connection being without groove but welding by both sides. The experiment is going on T joint welding specimen. By the comparison of two detection arrangement and the three probe method, it was obsrrved that double-crystal straight probe was the most sensitivity to incomplete penetration weld, transversal wave oblique probe the second. and single crystal straight probe the worse, transversal wave oblique probe is more accurate to quantitatively detect the size of incomplete-penetration weld.