A nanosphere or microsphere drug carrier, formulations comprising the drug carrier and the preparation method of the formulations and the use of the carrier are disclosed. The carrier comprises a biodegradable methoxy end-capped polyethylene glycol-polylactide block copolymersor a derivative thereof represented by formula (I) as the main carrier material: CH3O-[CH2-CH2-O]m-[C(O)-CH(CH3)-O]n-R (I).