Abstract: In this thesis, through theoretical analysis and referring to DL/T 820-2002 standard, inspection of small diameter austenitic steel tube weld at single side of the seam by using phased array method, was deeply studied. Deduced the principle of probe setting, ultrasound beam and other parameters configuration was deduced and skills of making DAC was introduced, and methods of measuring the echo amplitude and sizing the length of the defects were also raised. By means of technical analysis, it is indicated that, detection on small diameter austenitic stainless steel tube, equivalent to or better than detecting result can be achieved by phased array method than conventional UT.