A metal-organic framework/inorganic composite (ZIF-8@AMP) was synthesized by the in situ introduction of the active component ammonium phosphomolybdate (AMP) during the ambient solution-phase synthesis of the metal-organic framework (ZIF-8). The structure and properties of the composite were characterized using scanning electron microscopy (SEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR). Its adsorption performance for Rb⁺ and Cs⁺ in water was investigated. Results indicate that ZIF-8@AMP exhibited adsorption efficiencies of 93.5% and 95.6% for Rb⁺ and Cs⁺ within 30 min, with maximum adsorption capacities of 92.7 and 104.5 mg·g^-1, respectively. After five adsorption-desorption cycles, it maintained high adsorption capacity and achieved over 84.9% adsorption efficiency for Rb⁺ and Cs⁺ in actual brine samples. The adsorption of ZIF-8@AMP for Rb⁺ and Cs⁺ follows pseudo-second-order kinetics and the Langmuir adsorption isotherm, indicating an endothermic, entropy-increasing, and spontaneous process. The adsorption mechanism involves electrostatic attraction and ion exchange between ZIF-8@AMP and Rb⁺ and Cs⁺.