A water-soluble blocked isocyanate cross-linker was prepared, then it was used to improve durability of water- and oil-proof finishing on silk fabric. The results showed that the stability of the blocked isocyanate’s emulsion was better and the deblocking temperature of the blocked isocyanate was 67oC. As the blocked isocyanate was used in water- and oil-proof finishing on silk fabric, the durability of water- and oil-proof of the fabric was holding well after 10 launderings. Compared with the general cross-linkers (2D resin, TMM, HMM, etc.), the blocked isocyanate had no free formaldehyde release. And breaking strength, whiteness and handle of treated silk fabric had negligible decrease.