Abstract: Diatomite was used as raw material and prepared into a diatomite-based composite phosphorus removal agent by combining it with some combining steel slag. The agent was characterized with Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron micrograph (SEM). Besides, effects of dosage of the agent used, duration of the adsorption, pH value and temperature on performance of the agent were investigated by batch sorption experiments. Results show that combination with steel slag has brought about some changes in some parssads and in crystalline structure, creating new crystal phases. Static P-remvoving experiments demonstrate that the agent performed the best when the agent was applied at a rate of 2g·L^-1, into the wastewater, 5 in pH and 25 ℃ in temperature, for 1 h incubation. Evaluation of the experimental data in terms of adsorption kinetics reveals that the P adsorption kinetic behavior of the agent well fitted the pseudo-second-order kinetic model. Meanwhile, isothermal equations, such as Freundlich, Langmuir and Redlich-Peterson isotherms can be used to well describe the adsorption performance of the agent. The theoretical P saturation adsorption capacity of the agent is 1 428 mg•kg^-1, which indicates that the diatomite-based composite phosphorus removal agent can be used as a potentially efficient and environmental friendly absorbent material.