Abstract: To study the application of dynamic sonar in jellyfish monitoring in the intake areas of nuclear power cooling sources, from July 23 to August 5, 2023, the biomass of jellyfish was monitored using dynamic sonar at the monitoring station (JFQSK) at the cooling water intake of the nuclear power plant in the eastern Liaodong Bay. Simultaneously, the netting method was used for comparison. The results showed that the jellyfish biomass measured by the dynamic sonar method was consistent with the trends observed using the netting method. The biomass of jellyfish using the sonar method can be calculated based on four factors: the number of jellyfish shown in the sonar video, water depth, current speed, and the individual weight of jellyfish. According to the research, in the monitoring and early warning system for the protection of nuclear power cooling sources in the eastern coastal waters of Liaodong Bay, the yellow risk warning threshold for jellyfish monitoring using the dynamic sonar method is 350 kg/10⁴ m³, and the red risk warning threshold is 550 kg/10⁴ m³.