Abstract: This paper introduced the background of the national standard GB/T 39427—2020 Non-destructive Testing-Testing method for determining the size of Ir192 industrial radiographic source, explained the contents of the standard and expounded the verification test. The standard projected the image of Ir192 radiographic source onto the film, and determined the size of Ir192 radiographic source by measuring the side length of 2D image presented on the radiographs. The test results showed that the film radiography technology specified in this standard could accurately obtain the size of Ir192 radiographic source.