In recent years, there have been large-scale jellyfish outbreaks in the Bohai Sea in summer, which have greatly affected the water intake for cold source of Hongyanhe nuclear power station in Fuzhou bay and threatened the normal operation. This study aims at early warning of invasion of jellyfish, designs and develops acoustic monitoring system for cold source biological (jellyfish)by using ascientificechosounder (EY60,70kHz,Simrad), and carries out real-time monitoring of the echo of cold source biological entering water intake, so as to obtain the resource density of jellyfish from June to September 2019. The acoustic data is processed with a software of Echoview to calculate the average SV and detect the strength of the single target to calculate the daily average flux of the monitoring point. According to the monitoring results, the maximum and minimum daily average values of SV were -62.7dB and -80.0dB, respectively. The maximum and minimum daily average values of target strength are -37.2dB and -81.0dB, respectively. The maximum and minimum daily average values of flux are 5.36ind/(s•m2) and 1.2x10-5ind/(s•m2).Combined with the daily cleaning amount of the monitoring point back-end intercepting network and meteorological data, the comparative analysis is carried out to determine the index level of the acoustic warning for cold source biological flowing into the water intake according to the correlation between average flux and amount of cleaned net.