The concentration of calcium ion in cytoplasm is in strict control. Disequilibrium of calcium homeostasis will result in severe injury even death of cells. The roles of such disequilibrium in cells death resulted from exogenous factors, evidences of direct lethal effect of the disequilibrium on cell and effects of calcium ion in apoptosis were reviewedd. Mechanisms of these effects were discussed. In the end, on the basis of summary, a new way to inhibit cancer cell was suggested, by inducing disorder of calcium homeostasis selectively in cancer cells.