Red mud (RM) alone as an adsorbent for phosphorus shows unsatisfactory adsorption performance. This paper studied the wettability of katoite (the main component of RM) and its adsorption of phosphate. We also analysed the adsorption law of phosphate-containing water clusters on the katoite surface from bond length changes of the unit cell, adsorption equilibrium conformation, radial distribution function, interaction energy, adsorption isotherm and adsorption heat. found that kattenite has good wettability and the adsorption of phosphate is the result of van der Waals force and hydrogen bond.