The invention discloses a method for increasing S-adenosyl-L-methionine yield by saccharomyces cerevisiae genetic engineering. The method includes: replacing a GLC3 (glycogen branching enzyme gene) allelic gene on a chromosome of a saccharomyces cerevisiae strain with a G418 resistance gene according to a gene replacement method, and using a spore isolation method for obtaining a haploid with the gene GLC3 replaced only, so that a homozygote with gene GLC3 mutated is obtained. According to fermentation in 10L and 500L fermentation tanks, yields of ademetionine produced with mutant strains reach 7.93g/L and 8.35g/L and are increased by 15.1% and 24.7% respectively as compared with that of ademetionine produced with original strains.