Abstract: Chromosome karyotype analysis serves as a fundamental tool in cell genetics research, facilitating investigations into species evolution, classification, and the relationship between chromosome structure and function. This study employed classic methods, including colchicine solution soaking, low-concentration KCL treatment, Carnoy’s fixative, air-drying, and Giemsa staining, to observe and analyze the chromosome number and karyotype of the saltwater copepod Apocyclops royi. Additionally, it compared the slide-making effects of various colchicine concentrations, low osmotic pressure duration, and copepod dissociation methods. The findings revealed that the chromosome number of A. royi was 2n=12, consisting entirely of metacentric chromosomes, totaling NF=24 arms. Optimal slide preparation was achieved using a complete dissociation method with 0.10% colchicine concentration, 45-60 minutes of treatment, and 60-80 minutes of low-concentration KCL treatment. These research outcomes offer valuable insights for cell genetics research and germplasm identification and protection of saltwater copepods.