A methoxypolyethylene glycol-polylactic acid block copolymer is disclosed, the methoxypolyethylene glycol-polylactic acid block copolymer being a block copolymer formed by ring opening polymerization of D,L-lactide and methoxypolyethylene glycol. A mass ratio of the methoxypolyethylene glycol to the D,L-lactide is 1:0.55-0.65 or 1:0.73-0.89 or 1:0.91-0.99. A preparation method of the foregoing block copolymer is also provided. When the block copolymer is used as a carrier for preparing a drug micelle, the encapsulation efficiency of the drug micelle prepared after being re-dissolved by water can be greater than 90% at 12 hours.
