The utility model discloses a nuclear power station catch water overflow line for conventional thermoelectricity catch water's overflow line design can't realize keeping apart the gas that contains radioactive substance among the solution prior art, and then is not suitable for the technical problem of nuclear power, and this overflow line includes: with the catch water intercommunication, and set up flush connection below catch water's the minimum overflow control liquid level, with the flush connection intercommunication is used for keeping apart the isolation pipeline section that contains radioactive substance's gas among the catch water, with keep apart the pipeline section intercommunication for the drainage pipeline section of outside drainage when the overflow is protected. Realized carrying out overflow protection to nuclear power station catch water when that the gas that contains radioactive substance isolated catch water carries out the technological effect of keeping apart.