Abstract: According the characteristics of ship reactor, the RELAP5 models for its primary circuit and the secondary circuit were established, the ship reactor blackout accident under the economy headway condition was simulated using RELAP5/MOD3.2 code, and the mitigation effects of four different steam-exhaust schemes to the accident process were analyzed. The results show that the reasonable steam-exhaust scheme can mitigate the accident remarkably, and the delay time is about hour level; the less the steam is consumed, the longer the operation time of the equipment of the secondary circuit is, the longer the time of the heat sink of the primary circuit can last, and the slower the accident process will be. However, too little steam-exhaust flux will lead to steam generator (SG) water level excessively high or even brimming which will be a threat to normal operation of the devices in the secondary circuit. Meanwhile, there are many devices in the secondary circuit, and the limits to the minimum steam flux to operate the devices are different. Then, the most useful device with the lowest steam-exhaust flux should be chosen as the steam-exhaust operation equipment. The study can provide a reference for the emergent treatment during the ship reactor blackout accident.