The growth hormone with high biological activity modified by the double-strandedpolyethylene glycol at a single site and the preparation method thereof areprovided. ThePEGylated growth hormone has a higher biological activity and a longer half-life than theunmodified growth hormone. The composition comprising the PEGylated growthhormoneis useful in the treatment of the growth or development disorder such asgrowth hormonedeficiency, Turner syndrome etc..