Strontium-90 (??Sr) is a long-lived radionuclide produced by nuclear fission, which can be biomagnified through the marine food chain and cause damage to the human skeletal system and hematopoietic system upon long-term intake. Affected by marine discharge of nuclear wastewater and residual radioactive substances from nuclear tests, the pollution risk of ??Sr in marine environments persists.To develop a rapid and highly sensitive analytical method for the determination of 90Sr in seafood, a one step procedure for drying, carbonization, and ashing of 50 g samples was adopted. After nitric acid leaching, sample solutions were purified and concentrated using SrResin solid-phase extraction cartridges, followed by 90Sr quantification with an ultra-low background liquid scintillation counter (LSC). By optimizing the microwave ashing conditions of a large-capacity sample radioactive microwave ashing integrated system, SrResin purification and LSC counting were optimized by single factor experiments. The Method was comprehensively validated in terms of spike recovery, precision, and counting efficiencies for various sample matrices were corrected by the experimentally established quenching curve. The results demonstrated that the corrected counting efficiency for 90Sr exceeded 80.0% under optimized conditions. The spike recoveries of the four seafood matrices ranged from 82.31% to 91.69%, with relative standard deviations (RSD, n=5) of 2.14% ~ 4.78%. The method detection limit was 0.69 Bq?kg-1, far below the statutory limit of 10 Bq?kg-1 stipulated by Chinese national standard. Featuring easy operation, satisfactory purification efficiency and high sensitivity, the proposed method is suitable for rapid and accurate determination of 90Sr in seafood, and it can provide reliable technical support for efficient screening and risk assessment of radioactive contamination in seafood.