Abstract: SCF is not needed by life, but also vital for prevention from ionic radiation and repairing of damage by radiation. It is discovered that SCF can distinctively elevate the survival ratio of animal irradiated by lethal dosage, especially when it cooperates with hemocytogenesis factor and anti-radiation agents. SCF can inhibit apoptosis, promote cell cycle, accelerate proliferation and differentiation of many factors in marrow and peripheral blood, as may be the protective mechanism of SCF. It's ability of apoptosis inhibition may be associated with p53, Ca²⁺ influx, and mediated by caspase.