Objective The study aimed to explore the main forms of double minute chromosomes(DMs)in the cell cycle of colorectal cancer at different phases,and to clarify the replication and separation phases of DMs.Methods After using serum-free starvation to block the progression of cell cycle in colorectal cancer COLO 320DM cells,Calyculin-A was used to induce interphase cells to prepare karyotype samples through advanced chromatin condensation.COLO 320DM cells were treated with colchicine to ob-tain mitosis(M)phase cells for karyotype analysis.The karyotypes of cells at the early stage of DNA synthesis(G1 phase),the late stage of DNA synthesis(G2 phase),metaphase(M-mid),anaphase(M-late),and telophase(M-ter)of mitosis were observed and photographed under a regular optical microscope,and counted the number of DMs.Results DMs mainly existed in monotypic form at the G1 phase,M-late phase and M-ter phase of cells.In the G2 and M-mid phases of cells,DMs mainly existed in a diploid form.Conclusion Monomeric DMs undergo replication in the S phase and transform from monomers to diploids,while diploid DMs in the M-late phase complete separation and transition from diploids to monomers.