Based on the structural characteristics of the frame products of Pakistan railway train,this paper analyses and cracks the difficulties in the internal inspection technology of the girth weld of the cross-side beam interface of Pakistan railway train. The phased array ultrasonic testing technology scheme is established through experiments. The phased array ultrasonic testing of the girth weld of the cross-side beam interface of the frame can accurately detect the various types of internal defects in girth weld,full coverage of weld seam and detection of various internal defects are realized. The interference of structure can be eliminated according to the echo image display. It not only ensures the quality of weld seam,but also improves the production efficiency,and achieves satisfactory results. The application of phased array ultrasonic technology in girth weld detection is studied,which has been verified in practical testing.