The invention relates to a seawater radionuclide analysis pretreatment method. The method includes 1, adjusting the pH value of the acidity of a seawater sample to range from 1 to 2; 2, adding a mixed carrier into the seawater sample; 3, adding 0.15 to 0.25g ammonium phosphomolybdate and 0.15 to 0.25g ammonium sulfate in the seawater sample per liter; 4, depositing and drying; 5, adjusting the pH value of the acidity of the filtrate to range from 8 to 10; 6, depositing and drying; 7, depositing and combining. According to the mixed carrier, Rho (Cs+)=5 to 7mg/mL, Rho (Co2+)= 18 to 22mg/mL, Rho (Fe3+)=38 to 42mg/mL, Rho (Ba2+)= 38 to 42mg/mL, and Rho (Pb2+)= 38 to 42mg/mL. By the aid of the method, gamma nuclide and total alpha and beta analysis and combined sample preparation can be implemented, the problem of influence by residue is avoided, the method is simple and easy to implement, and the accuracy is improved greatly.