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: CH 3 O-[CH 2 -CH 2 -O] m -[C(O)-CH(CH 3 )-O] n -R (I).