The invention relates to an enzyme for synthesizing metabolic uridine acid from orotic acid nucleotide in the presence of 'Bailing' producing strain Cordyceps sinensis Hirsutella sinensis , a gene encoding the enzyme, an application of the enzyme, and an application of the gene. The enzyme is uridylic acid synthetase, the amino acid sequence of the enzyme has a homology of above 90% with an amino acid sequence represented by SEQ ID No.1, SEQ ID No.3 or SEQ ID No.5, and the sequence of the coding gene of enzyme has a homology of above 90% with a nucleotide sequence represented by SEQ ID No.2, SEQ ID No.4 or SEQ ID No.6. Detailed researches of the metabolic pathway of the uridylic acid synthesized from the orotic acid nucleotide are carried out in principle, cloned DNA containing the nucleotide sequence provided by the invention can transferred to engineering bacteria through a transduction, transformation and combined transfer method, and the adjustment of the expression of uridylic acid biosynthetic gene realizes the high expression of host uridylic acid, so an effective way is provided for enlarging the output of the uridylic acid, and the enzyme has a great application prospect.