Abstract: A radiochemical pure ~(138)Cs solution must be isolated from fission products,for more precise decay data of short-life nuclide ~(138)Cs are abtained.Based on "twice delay separation method",an one-hour separation procedure for ~(138)Cs from fission products is designed and examined,which combined "deflation",Cs_3Bi_2I_9 precipitation and Cs_4(Si(W_3O_(10))_4)precipitation.The chemical recovery of ~(138)Cs is about(74±1)%.The decontamination factors for main γ-emitters are higher than 1×10~3 and no contamination is found.