Abstract: The typical defects of air hole, slag, incomplete fusion, incomplete penetration and crack in tube-shell fillet weld were studied in this paper. Firstly, the basic information of the fillet weld joint and the basic principles of phased array technique were introduced. Secondly, artificial test blocks containing the above defects were designed and manufactured. In addition, the artificial test blocks were tested, and the detection ability of conventional phased array technique and full focus technique for the above five defects was compared. The testing results show that the fully focus technique has a higher defect detection rate and detection resolution. The defect positioning and quantitative error is smaller compare to the conventional phased array technique, indicating that the fully focus technique can be applied in engineering.