Abstract: The cleaning reagent on decontamination of the primary loops of reactors was studied. For rapid erosion of basic material, the composition of destroyable decontamination reagent and chelating agent were done. The test for primary reagent and selection experiment of erosion reagent were done. KMnO4 was selected for decontamination reagent and the concentration and flow velocity were tested. According to the whole experiment the factors on decontamination of the primary loops and the best cleaning reagent were ascertained.