Abstract: Ammonium molybdophosphate(AMP) is a kind of heteropoly salt with strong selectivity and ion exchange capacity for ¹³⁷Cs. But the small particle size and poor hydromechanical property of AMP, makes it difficult to separate in the later stage. In view of the above problems, AMP was loaded on the expanded perlite to prepare the composite inorganic ion exchange material, and then the adsorption mechanism for Cs⁺ were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), Fourier transforms infrared spectrometer(FTIR) and electron probe microanalyzer(EPMA). These results show that the stable adhesion of AMP on the expanded perlite/AMP composites is a physical process. The adsorption of Cs⁺ by the composite material reaches the adsorption equilibrium at 120 min. Its maximum saturated adsorption capacity is 13.21 mg/g. The adsorption process conforms to the quasi-second-order kinetic equation(r²=0.99). The isothermal adsorption process conforms to the Langmuir model(r²=0.99), which is a monolayer of chemisorption process with homogeneous adsorption points. The coexisting ions Al³⁺, Fe³⁺ and Ni²⁺ have little effect on the adsorption of Cs⁺, indicating that the composites have some selectivity for the adsorption separation of Cs⁺.