The invention relates to a method for synthesizing L-(+)-selenomethionine, which comprises the following steps: reacting L-(+)-methionine with iodomethane to generate a sulfur salt, hydrolyzing the sulfur salt in the presence of an inorganic base to obtain homoserine, adding an acetic acid solution of hydrogen bromide into the homoserine, and reacting to obtain bromo-L-(+)-homoserine hydrobromide;reacting bromo-L-(+)-homoserine hydrobromide, methanol and thionyl chloride to generate bromo-L-(+)-homoserine methyl ester hydrochloride; reacting brominated L-(+)-homoserine methyl ester hydrochloride, selenium powder, lithium methide and a boric acid ester, and then carrying out hydrolysis under alkaline conditions. L-(+)-methionine is adopted as a raw material, the raw material is wide in source and low in price, and has chirality, and the problems that a chiral center is introduced in follow-up synthesis and high stereoselectivity is kept can be directly solved. The synthetic route provided by the invention has the advantages of readily available raw materials, mild reaction conditions, easiness in separation and purification and the like.