The invention discloses a nuclear radiation resistant non-marking rubber product for sealing a nuclear island, which is prepared from a main material and a joint material, wherein the main material is prepared from the following materials in part by weight: 100 parts of ethylene propylene diene monomer, 4 to 8 parts of active agent, 1 to 5 parts of vulcanizing agent, 1 to 5 parts of accelerator, 0.5 to 3 parts of anti-aging agent and 15 to 35 parts of complex; and the joint material is prepared from the following materials in part by weight: 100 parts of ethylene propylene diene monomer, 3 to 7 parts of active agent, 1 to 4 parts of vulcanizing agent, 1 to 4 parts of accelerator, 0 to 1 part of scorch retarder, 3 to 7 parts of inert filler, 1 to 5 parts of anti-aging agent and 15 to 35 parts of complex. In addition, the invention further provides a method for preparing the non-marking rubber product. No marks visible to naked eyes remains at the joint of the non-marking rubber product, the convex and concave defects in the joint and in a non-joint position are within the specified limit of tolerance, and the tensile strength and the elongation at break in the joint and in the non-joint position are the same, so that the application requirement of sealing the nuclear island is satisfied.