This study investigates the impact of expansion agent (EA) and glass fiber (GF) on the dynamic splitting tensile properties of seawater–sea-sand concrete (SSC). The dynamic Brazilian disc test was conducted using a Split Hopkinson Pressure Bar (SHPB) device at various strain rates to evaluate the effects of EA and GF on the mechanical properties of SSC. The results show that the strain rate significantly affects the dynamic splitting tensile behavior of EA and GF-reinforced SSC, indicating strong strain rate sensitivity. The combination of EA and GF enhances the energy absorption capacity under impact loading, maintaining the morphological integrity of the concrete. However, the dynamic splitting tensile strength obtained from the Brazilian disc test exhibits a significant overload effect, which cannot be ignored. The addition of 6% EA and 1% GF to the SSC showed a synergistic enhancement in dynamic splitting tensile properties. The study also analyzed the damage modes, strain rate effects, and energy dissipation capabilities of the specimens, providing insights into the dynamic splitting performance of EA and GF-reinforced SSC. The findings support the development of SSC with excellent dynamic splitting tensile properties, which are crucial for marine structural engineering applications.This study investigates the impact of expansion agent (EA) and glass fiber (GF) on the dynamic splitting tensile properties of seawater–sea-sand concrete (SSC). The dynamic Brazilian disc test was conducted using a Split Hopkinson Pressure Bar (SHPB) device at various strain rates to evaluate the effects of EA and GF on the mechanical properties of SSC. The results show that the strain rate significantly affects the dynamic splitting tensile behavior of EA and GF-reinforced SSC, indicating strong strain rate sensitivity. The combination of EA and GF enhances the energy absorption capacity under impact loading, maintaining the morphological integrity of the concrete. However, the dynamic splitting tensile strength obtained from the Brazilian disc test exhibits a significant overload effect, which cannot be ignored. The addition of 6% EA and 1% GF to the SSC showed a synergistic enhancement in dynamic splitting tensile properties. The study also analyzed the damage modes, strain rate effects, and energy dissipation capabilities of the specimens, providing insights into the dynamic splitting performance of EA and GF-reinforced SSC. The findings support the development of SSC with excellent dynamic splitting tensile properties, which are crucial for marine structural engineering applications.