An atomic group model of the disordered binary alloy Rhx-Pt1-x has been constructed to investigate surface segregation. According to the model, we have calculated the electronic structure of the Rhx-Pt-x alloy surface by using the recursion method when O atoms are adsorbed on the Rhxx(110) surface under the condition of coverage 0.5. The calculation results indicate that the chemical adsorption of O changes greatly the density of states near the Fermi level, and the surface segregation exhibits a reversal behaviour. In addition, when x＜0.3, the surface on which O is adsorbed displays the property of Pt; whereas when x＞ 0.3 it displays the property of Rh.