Abstract: In an international cooperative project, ultrasonic testing of steel plate was carried out. There was a big difference in the testing results as conducted by Chinese side and German side, some of which were up to 20 dB. After comparing and analyzing the testing standards, methods and testing equipment of two countries, the cause was found out. Proposal was made to refer to steel plate AVG curve method recommended by EN 10160 standard: drawing AVG curve of the reflected wave of flat-bottom hole and AVG curve of the bottom wave at the same time, so that the coupling state in the steel surface could be observed at any time during UT, regardless of the use of soft or hard protective film probe.More consistent testing results could be received, and it was therefore an effective method for flaw assessment in steel ultrasonic testing.