The present invention relates to an amphiphilic block copolymer represented by formula I, a preparation method thereof, and a nanomicelle drug delivery system formed from the copolymer and a poorly soluble drug. The amphiphilic block copolymer includes a hydrophilic chain segment, a hydrophobic chain segment, and a linker for linking the hydrophilic chain segment to the hydrophobic chain segment. The linker contains an unsaturated structure, which can enhance the interaction between the poorly soluble drug and the copolymer to improve the drug loading ability and stability of the nanomicelle. The invention also relates to a nanomicelle drug-loading system, a preparation method thereof, and the use of the nanomicelle drug-loading system for preparing medicines for treating tumors, inflammation, diabetes, central nervous system diseases, cardiovascular diseases, and psychological disorders.