The invention discloses a new saccharomyces cerevisiae strain and a feed additive and premix containing the same. The collection number of the new saccharomyces cerevisiae strain K1 provided by the invention is CGMCC No.6560. The invention also provides a livestock and poultry feed additive containing the strain. By feeding the livestock and poultry, particularly the young livestock and poultry with the daily ration added with the livestock and poultry feed additive provided by the invention, the diarrhea occurrence rate is relatively low, thus the death and culling rate is reduced, the production performance is greatly improved, and a good growth foundation is laid for the further growth of the livestock and poultry.