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.
