The invention relates to a passive safety injection system for a nuclear power station. The passive safety injection system comprises an impounding reservoir in a safe case, a water supply pipe, a water supply isolation valve, a passive safety injection turbine pump, a pressure release valve at the secondary side of an evaporator, a steam discharging pipe, a safety injection pipe, cooling water and a safety injection isolation valve, wherein the bottom of the impounding reservoir in the safe case is higher than the top of a U-shaped pipe; the cooling water is stored in the impounding reservoir in the safe case; the impounding reservoir in the safe case communicates with the passive safety injection turbine pump through the water supply pipe and the water supply pipe isolation valve arranged on the water supply pipe; the passive safety injection turbine pump communicates with the secondary side of the evaporator through the steam discharging pipe and the pressure discharging valve of the secondary side of the evaporator arranged on the steam discharging pipe, and communicates with the secondary side of the evaporator through the safety injection pipe and the safety injection isolation valve arranged on the safety injection pipe; when the liquid level of the secondary side of the steam generator is reduced to the low liquid level, the reliable passive water supplementation is performed, so that the secondary side of the steam generator continuously unloads the afterheat of a reactor core of a reactor.