A Saccharomyces cerevisiae expression system and a construction method and application thereof, including an expression vector which includes, from 5 to 3, a YEplac195 plasmid backbone, an exogenous gene expression cassette, and a selective marker gene expression cassette. The exogenous gene expression cassette includes from upstream to downstream an rDNA promoter, an internal ribosome entry site (IRES) sequence, an exogenous gene expression cassette, a poly(T) sequence, and an rDNA terminator. The selective marker gene expression cassette includes a promoter, a selective marker gene, and a transcription terminator.