provided are a polycaprolactone - polyphosphate block copolymer , a liquid composite formed by the block copolymer , a nucleic acid preparation , preparation methods for the copolymer and the liquid composite , and the use of the copolymer and the liquid composite in a nucleic acid medicine delivery system . the block copolymer prepared using the present invention has good biocompatibility , low cytotoxicity , and good biodegradability . the micelles provided in the present invention self - assemble into nano - particles in an aqueous solution , and have good stability , biocompatibility , and biodegradability , and low cytotoxicity . the preparation method is simple , has high repeatability , as a vector can protect small nucleic acids such as sirna from biodegradation , can combine with the scale effect of nano - particles , and can be used for treating different diseases . additionally , bonding targeting groups enable specificity recognition of different cancer cells .