The present invention provides a doped semiconductor nano-crystalline and its preparing method. The doped semiconductor nano-crystalline is MnSe/ZnSe/ZnS, using Mn doping with ZnSe semiconductor nano-crystalline as a case, covering with core-shell structure nano-crystalline of ZnS layer. The covering range of the photoluminescence peak of the semiconductor nano-crystalline is 570-610nm, having better monodispersity, the quantum yield is more than 50%, the fluorescence stability is higher. The invention has a simply synthetic method, simply doped process, convenient control for doped quantity,avoiding the use of combustible and explosible medicine at the same time.