Abstract: A new ultrasonic phased array inspection system for pressure vessel is designed in this paper. This device can automatically scan the weld of pressure vessel. Aiming at the NDT process of a certain nozzle weld, the phased array ultrasonic testing process of the system is simulated by CIVA simulation software. The sound field simulation results show that the selected phased array probe and its set focusing rule can effectively cover the entire weld thickness area, with part of the inspection area coincides, and the ideal focusing inspection effect can be achieved. The defect response simulation results show that the defect response echo of surface defects and buried defects with different depths is greater than the recording standard(DAC-12.0dB), and the signal-to-noise ratio meets the requirements, which can be effectively detected. The simulation results provide a reference for the design and optimization of ultrasonic detection technology.