The invention provides a method for synthesizing ZnxCd1-xSe (x is more than or equal to 0 and less than or equal to 1) and ZnxCd1-xSe/ZnSe, ZnxCd1-xSe/ZnS and ZnxCd1-xSe core/shell structured semiconductor nanocrystals thereof by using long-chain fatty acid salts of cadmium and zinc as precursors of cadmium and zinc, which is the most economical and environment-friendly method for synthesizing high-quality ZnxCd1-xSe and related core/shell structured semiconductor nanocrystals thereof currently. The method avoids using tributylphosphine (TBP) or trioctylphosphine (TOP) dissolved elementary selenium as the precursor of selenium currently in the world, but adopts octadecylene (ODE) dissolved elementary selenium as the precursor of selenium; and the obtained nanocrystals have the quality equal to that of nanocrystals which are synthesized when the TBP or TOP dissolved selenium powder is used as the precursor of selenium. The method is called a phosphine-free method, has the advantages of simple synthesizing process, good repeatability, safety, environmental protection, no need of glove box, and cost conservation of over 60 percent. The synthesized ZnxCd1-xSe and related core/shell structured nanocrystals have a fluorescence range of between 400 and 650nm, and have the advantages of uniform particle size distribution, high efficiency of fluorescent quantum yield (40 to 70 percent) and narrow full width at half maximum. The method is also suitable for synthesizing the ZnxCd1-xS, HgxCd1-xSe, ZnxCd1-xTe nanocrystals and related core/shell structures thereof. More importantly, the method can synthesize high-quality nanocrsytals on a large scale, and has enormous application value both in laboratory synthesis and industrial synthesis.