The invention discloses a method for screening and detecting a single-nucleotide polymorphic site G642A of marsupenaeus japonicus, and relates to the marsupenaeus japonicas. A specific primer is designed by a PAMSA method, so that verification and genotyping of a single-nucleotide polymorphic mark of the marsupenaeus japonicas can be conveniently and quickly performed through polyacrylamide gel electrophoresis; the method has the advantages of low screening and detecting expense, high simplicity, convenience and quickness in operation and the like; by the method, parentage determination of the marsupenaeus japonicas, establishment of a genetic linkage map, and other researches are facilitated; under the condition that information of the single-nucleotide polymorphic site of a genome DNA of the marsupenaeus japonicas is unknown, through transcriptome mixed sample sequencing, and by virtue of bioinformatic analysis, the single-nucleotide polymorphic site G642A is screened; the specific primer is designed by the PAMSA method, so that the single-nucleotide polymorphic site G642A of the marsupenaeus japonicas can be conveniently and quickly detected, verified and genotyped through the polyacrylamide gel electrophoresis, the screening and detecting expense is low and the operation is simple, convenient and quick.