Using the genome DNA of the strain YA of pseudorabies virus(PRVYA) as template and with flanking primers, the TK gene fragment was amplified by polymerase chain reaction (PCR). The expected size of the fragment was obtained, and it was then cloned into the PMD18-T vector. The recombinant plasmid PMD18-TK was identified by PCR, restriction enzyme analysis and sequencing, which completely proved its validity.