Abstract: Analysis was made of the attenuation characteristics of two kinds of materials hastelloy C-276 and 16Mn to the X-ray and their radiographic equivalence coefficient range was initially concluded. Then, the radiographic equivalence coefficient in the applied thickness range of the two materials was obtained by testing. Through analyzing and comparing three RT technologies of large thickness ratio workpiece, it was determined to use thickness compensation technology, and accordingly make thickness compensation block used in the actual detection, and thus leading to solve the problem of process parameters’ determination and film quality control in RT work.