Abstract: In regard to the problem due to respective choice of testing parameters in common radiographic testing, the requirement for two technique classes in JB/T 4730: 2005 standard is analyzed. Using exposure curve and film characteristic curve equations, together with technique classes, the function relation between geometric penetration parameters and physic penetration parameters is established. The parameter conditions in which values of penetration thickness ratio K and film density tolerance ΔD0 are satisfied simultaneously are discussed. Based on the above mentioned ones, an optimized method for choice of testing parameters is proposed, and is verified by the experiment. The results show that two technique classes in JB/T 4730: 2005 standard can be reached by the optimized method.