Abstract: Ce was used to simulate Pu,the mixed solution of U,Ce,Zr and Ru was used to simulate the spent nuclear fuel solvent,and dibutyl phosphate（HDBP） was used to simulate the degradation products.The formation of interfacial dirt in the spent nuclear fuel solvent was studied by single-stage extraction,the basic composition of the interfacial crude was qualitatively analyzed,and the causes of the interfacial crude were discussed.The results show that uranium,zirconium and cerium will all be involved in the formation of the interface crude;uranium and zirconium could promote the generation of interfacial crude,while cerium had little effect on the generation of the interfacial crude,while acidity played a reverse role on the generation of the interfacial crude.