The present disclosure may disclose a multi stage safety injection device and a passive safety injection system having the same, including a safety injection tank formed to contain coolant to be injected into a reactor vessel by a gravitational head of water when an accident occurs in which the pressure or water level of the reactor vessel is decreased, a pressure balance line connected to the reactor vessel and safety injection tank to form a pressure balance state between the reactor vessel and the safety injection tank, a safety injection line connected to a lower end portion of the safety injection tank and the reactor vessel to inject coolant to the reactor vessel in a pressure balance state between the reactor vessel and the safety injection tank, and a flow control line extended from the safety injection line to an inner portion of the safety injection tank, and provided with safety injection ports into which coolant is injected at predetermined heights, respectively, to reduce the flow rate of coolant injected into the reactor vessel step by step according to the water level reduction of the safety injection tank, in order to inject coolant to the reactor vessel at multi stages.