Abstract: The aggregation or outbreak of marine organisms can block the cold source water system of nuclear power plant, bringing high risk to its normal operation.In recent years, it has been widely reported that some nuclear power plants were forced to close due to the aggregation or outbreak of marine organisms.So, it is urge to compile a catalogue of risk marine organisms for nuclear power plant in order to ensure the safe operation of its cold source water system.The research from June to November of 2015 in the adjacent waters of the Hongyanhe River showed that high risk marine organisms included Ulva linza, Ulva pertusa, Aurelia aurita, Nemopilema nomurai, Pleurobrachia globose, Acetes chinensis, etc. . The risk level is "High" when relative density of moon jellyfish is greater than or equal to 500 ind./(net.h), called the red level; level "Medium" is when the relative density is more than 300 but less than 500 ind./(net.h), called the yellow level; level "Low" is greater than 100 and less than 300 ind./(net.h), called the blue level.This study has implications to the monitoring plan, early warning technology, and preventive measures of the risk marine organisms for the nuclear power plant.