Abstract: The methyl 3H TdR is prepared by a catalytic reaction of substituting tritium based on (5 F 3) TdR as precursor and PdO/BaSO 4 as catalyst. The optimum conditions of tritating, separating and purifying, as well as the store of the labeled compound are selected. The specific activity of the tritation is 9.1 TBq/g which is two times higher than those prepared by other method. The radiochemical purity of the tritation is more than 95%, and the tracer sensitivity can be improved more than 70%.