Abstract: According to the characteristics of the product and dielectric properties of GQ80 type railway tanker,present paper discusses the necessity of nondestructive testing of GQ80 tank butt joint.Combining the design requirements with nondestructive testing specifications by North American railway tank car and the domestic liquid dangerous goods tank transportation tool,it further clarifies the choice of X-ray detection method according to the quality standards of grade III of JB/T 4730.2-2005.It also provides reason of the detection ratio being not less than 10%,thus providing a scientific basis for the railway tank car manufacturing industry to implement nondestructive testing.