Abstract: In order to simply, quickly and efficiently evaluate the impact of nuclear power plant operation on the surrounding marine environment, a cobalt sulfide coprecipitation method was established to rapidly analyze the gross beta activity excluding 40K in seawater. The effects of constant temperature, initial pH value of solution and constant temperature time on the enrichment rate of Ag, Fe, CO and Sb in the analysis of gross beta activity excluding 40K in seawater by cobalt sulfide coprecipitation method were studied. It is determined that the pH value of the supernatant after cooling is the key factor affecting the enrichment rate of radionuclides. The detection efficiency of 60Co and 137Cs on the proportional counter was studied, and 60Co is recommended as the calibration source for the efficiency calibration of this method. The detection limit is 0 005 7 Bq/L for 3 0 L seawater samples. The analysis results of gross beta activity excluding 40K in actual seawater show that the range is 0 083 0 113 Bq/L. The spiked experimental results show that the maximum relative deviation between the measured value and the spiked value is -8 33%, which confirms the accuracy of this method.