Provided are a eukaryotic expression system and its applications. The eukaryotic expression system has a recombinant plant cell. The recombinant plant cell includes a first vector and a second vector. The first vector expresses a fusion protein containing an Asia tospoviral common epitope. The fusion protein containing Asia tospoviral common epitope consists of an amino acid sequence as set forth in SEQ ID NO. 1, and a predetermined protein fragment connecting to the Asia tospoviral common epitope. The above eukaryotic expression system is useful for monitoring the interaction between proteins via use of a specific peptide to tag the predetermined protein and demonstrates high sensitivity and stability.