Abstract: The clam Cyclina sinensis is an economically important shellfish in China, and it is urgent to explore the excellent germplasm resources of C. sinensis. This requires the support of accurate genetic and biological basic materials. In order to accurately understand the number of chromosome and its karyotype composition of C. sinensis, we prepared diploid chromosomes and haploid chromosomes from the gill tissue and mature gonad of C. sinensis, respectively. The results showed that the chromosome number of diploid was 2n = 38 and haploid was n = 19. On the basis of the above experiments, the well dispersed visual field of diploid chromosomes was measured by microphotography, and the karyotype was analyzed. The result of experiment indicates that the karyotype is 11m+6sm+2st, NF=76, and no heterosome and satellite chromosome were found. In this study, the haploid chromosome was successfully prepared by the mature gonads of the calm, which was to provide a new idea for molluscs chromosome studying. Moreover, the new discovery on chromosome number and karyotype of C. sinensis makes up for the results of previous studies, which was 2n = 36. And it contributed to the more correct direction of phylogenetic research and genetic research of bivalve molluscs, also provided more scientific basis for whole genome sequencing assembly of C. sinensis.