The invention relates to a detection technology by ptssr17 microsatellite DNA markers in a blue crab. The technology is characterized in that: first, genome DNA of the blue crab is extracted and diluted to reserve; second, by utilizing a ptssr17 microsatellite core sequence in a genomic library of the blue crab, specificity primers are designed at the two ends of the sequence thereof; third, the genome DNA of different geographic groups of the blue crab or individuals in a blue crab group is processed through the PCR amplification by using the primers, and PCR products are processed through the modified polyacrylamide gel detection; finally, bands which are generated in the products are utilized for analyzing so as to determine the genotype of each individual, thereby obtaining a polymorphic map on the enormous genetic variation of the blue crab in the a ptssr17 core sequence area. The polymorphic map that the ptssr17 genetic mark gene locus of the blue crab shows the enormous genetic variation can be obtained rapidly; the method is simple and convenient; the each individual genotype of the blue crab at the locus can be detected intuitively from the obtained results. The detection technology is mainly used in the genetic marks among the blue crab groups, the genealogical identification, the genetic map construction, etc.