Abstract: This paper analyzes the weld seam of the frame part of the EMU which needs to be inspected but has a special structure, and introduces an application case of ultrasonic phased array in detecting weld crack and non-fusion defects in the process of new system and overhaul frame of EMU. It describes in detail the determination process of the scheme, the selection method of the relevant technological parameters, such as the probe and the wedge, the emitting wafer, the angle range, the step bias, and the process of feasibility verification of the scheme. The results show that ultrasonic phased array detection technology can be used to detect abnormal weld of the frame of EMU.