Fe-Mn oxide/diatomite composite was prepared by oxidation reduction and coprecipitation techniques. The effects of raw material ratio, reaction temperature, calcination temperature and solution pH on adsorption phosphate property of composite were investigated with an analysis based on adsorption isotherm, XRD and IR. The results indicate that adsorption capacity of composite prepared from 2.5 g diatomite, 1.0 mmol manganese, 3.0 mmol ferric iron and 3.0 mmol iron (Ⅱ) is 10.84 mg/g under the condition of 20℃ and pH equal to 6, increasing 3.6 times compared with diatomite. Precipitation reaction temperature is negligible and calcination of 400~500℃ is beneficial to adsorption. Adsorption capacity decreases with increase of pH, and inner-sphere complexing and electrostatic attraction on surface are jointly driving force for adsorption of phosphorus at lower pH. At high pH, inner-sphere complexing and electrostatic attraction decrease, co-adsorption with inner-sphere complexing promotes adsorption, and the total effect is the declining of phosphorous adsorption. Adsorption isotherms are well consistent with Langmuir and D-R equation and R-P equation, the saturation adsorption capacities are 34~37 mg/g and the average adsorption energies are 9.9~11.3 kJ/mol,revealing single and multiple layers adsorption with the coexistence of physical and chemical actions.