By UV-sunlight and ultrasonic compound mutagenesis method was used to select beer yeast, and its influence on beer brewing was studied. The research shows that the optimum strain Y7 obtained by UV-sunlight and ultrasonic waves for compound mutagenesis and screening of beer yeast strains with low-diacetyl production were genetically stable after 10 generations. Compared with the original microbe, there was no significant difference in the content of diacetyl and other substances in beer brewed by this strain (P>0.05).And the difference was significant (P<0.0001),and it can reduce the diacetyl account by 33.04%.And the alcohol content can be improved by 2.2%, and the fermentation degree was improved by 3.6%.The research on the difference of brewing technology and fermentation cycle of the mutant strain, shows that there were significant differences in fermentation index and fermentation cycle (P<0.0001),and the strain can greatly improve the beer fermentation capacity and the ability of anti-miscellaneous bacteria. The application of mutant strain Y7 in beer enterprises can greatly improve beer fermentation ability and resistance to miscellaneous bacteria, and improve beer flavor quality. And it can also improve the quality of beer flavor and shorten the main fermentation cycle by 1/3.