Abstract: The types, position and functions of artificial defects in automatic ultrasonic testing reference block of the 2nd west-east gas pipeline were introduced, and the requirements of reference block for probe quantity were analyzed. Two group probes could satisfy calibration requirement of surface and internal vertical flaws. Through mathematical treatment method ultrasonic probe effective acoustic beam width was calculated. The results showed that two group probes could not cover the whole weld area when pipe thickness was beyond 25mm. Now it was necessary to perfect the reference block.  3.2mm horizontal drilling should be added into reference block at the weld center along the length direction, in order to check detection capabilities of detecting system in thickness direction accurately.