The invention relates to a site-specific mutagenesis modified yeast dipeptidyl peptidase III. The yeast dipeptidyl peptidase III is an isolated mutant produced by making a plurality of amino acid substitutions in a wild type yeast dipeptidyl peptidase III derived from Saccharomyces cerevisiae S288c having an amino acid sequence of SEQ ID NO. 1, said amino acid substitutions comprising substitutions at positions 570, 572 and 574, so that the site-specific mutagenesis modified yeast dipeptidyl peptidase III is an enzyme having an oxidative decomposition activity on 6-methoxy-bifuran coumarin. The site-specific mutagenesis modified yeast dipeptidyl peptidase III can be used in preparation of a feed and additives thereof, and a food and additives thereof, in which 6-methoxy difuran coumarin is eliminated, and can be used in preparation of a medicament for preventing diseases induced by 6-methoxy-difuran coumarin.
