Abstract: It is difficulty of nondestructive quantitative evaluation of axial gap in small-diameter pipe socket welding. On the basis of selecting typical socket welding pairs, the CIVA simulation platform was used to simulate and optimize the frequency and axial gap acoustic field response of the probe. Calibration test blocks and specialized scanning fixtures were designed, followed by the development of a phased array ultrasonic measurement process of axial gap for socket welding, and process validation was conducted on simulated test blocks. The results showed that the simulation results of the designed and developed phased array ultrasonic measurement process of axial gap for socket welding were almost consistent with the measured results of the simulated test block. The maximum error rate of 1~3 mm axial clearance measurement was 3% and the process could be used for quantitative evaluation of axial gap.