【Objective】 Sagittaria trifolia is an important horticultural and cash crop in China. Identification of genome size and conducting karyotype analysis are essential for genome research and molecular genetics of S. trifolia. At this stage, the genome size of the S. trifolia. and chromosome morphology's are still unclear, the present study with a view to provide more cytological references to S. trifolia. breeding and species evolution. 【Methods】The study was conducted using flow cytometry, fluorescence in situ hybridisation and with reference to the lysate formulation, probe configuration, to identify the genome size of the root tips of S. trifolia. arietinum variety 'Zijinxing' (ZJX) and to analyze and observe the chromosome morphology of the root tips.【Results】 (1) The tested cecropia was a diploid plant, and the genome of 'Zijinxing' cecropia was about 16 Gb. (2) Using DAPI fluorescence staining, the number of chromosomes was obtained to be stable and in perfect agreement with the results of telomeric fluorescence in situ hybridization, which were all 22, and the chromosome types were middle mitotic (metacentric chromosome), near-middle mitotic (submetacentric chromosome), and proximal mitotic (acrocentric chromosome), with the largest number of proximal mitotic and no follower was found; and the formula for the karyotype was 2n=2x=22=6m+4sm+12st, which belonged to the Stebbins type. The karyotype formula was 2n=2x=22=6m+4sm+12st, which belonged to type 3B of Stebbins type, and the karyotype asymmetry coefficient was 99.13. 【Conclusion】 The study concluded that the genome of S. trifolia. was of medium size, with a highly asymmetric karyotype and a high degree of evolution.