The effect of antibacterial peptide CM4 component act on the K562 cancer cells in vitro is reported. The tests showed that: the purified antibacterial peptide CM4 component can kill human myelogenous leukemia cancer (K562). The observation of ultrastructure of the cancer treated with the antibacterial peptides by using the scanning and transmission electron microscope and the microfault picture analyses of laser confocal microscope. The results showed that the pruified antibacterial peptides brought about a series of pathological changes on cancer cells. As a result, the cells were high swelling, plasmolysis and disorders in subcellular and membrane structrue occurred, outer coat of cell dissolved, thus appearing irregular holes opening in a utensil and serious broken of skeleton structure of the cells. The membrane structure of some areas was broken and injured and intracellular substances leaked out. As a result, the cells disintegrated into small fragmants and died.