CdSe cores with the particle size over 7.5nm are successfully synthesized by me ans of two-steps injection of the Cd precursor.Efforts are made to restrain the Ostwald ripening process during the quantum dots grown up. With optimized synthesis conditions,such as the injection speed and molar rat io of precursor,the prepared CdSe cores show zinc blend structure with larger core size.Though the luminous efficiency of the prepared core is 15%,the efficiency increases drastically up to 43% after forming the ZnCdS shell on the core.Conditions of shell coating are also b een optimized,and the obtained quantum dots with emission wavelength exceeded 660nm.The obtained deep-red QDs with high efficiency and optical stability are e xpected to find their application in the field of plant′s illumination.