Abstract: The difficulties in the ultrasonic detection of the fillet welds in power plant boilers are discussed, a phased array ultrasonic testing solution is proposed. By using phased array ultrasonic testing method, the prefabricated defects were successfully detected through the production of welding simulation samples and compared with the results of wire cutting. The results show that the test results are better and the effectiveness of the inspection process is also verified. It can be used as a reference for phased array ultrasonic testing applied to the fillet weld of the tube seat.