The invention relates to the field of fermentation, and particularly provides a method for fermenting L-lysine. Acetate is added into lysine primary seed culture media, lysine secondary seed culture media and lysine fermentation culture media, and formulas and fermentation processes for the various culture media are optimized. The method has the advantages that growth of lysine producing thalli and synthesis of lysine can be promoted, accordingly, the endpoint lysine content, the total acid content and the saccharic acid conversion rate can be obviously increased, and the fermentation periods can be obviously shortened.