Abstract: The acid and alkali circulation utilization of foam can be realize due to the exist of pH-sensitivity carboxyl groups in oleate. With methods of Warning-blender, acid-base titration test, surface tension and interfacial tension test and microscopic analysis, etc., the effects of pH values change on aqueous solution properties of oleate, ionization degree of carboxyl group of oleate, and foaming properties of oleate were analyzed. Meanwhile, six foam circulation experiments have been carried out, and defoaming mechanism was discussed through explanation of microscopic phenomena, spreading and bridging mechanisms. The results show that carboxyl group of oleate can easily lose or receive protons to realize the reversible interconversions between active and inactive, further to realize circulation utilization of foam. Also, the defoaming mechanism analysis suggests that the invasion of hydrogen ions can lead to form water insoluble oleic acid of foam structure of oleate, and into the foam liquid films structure, facilitate liquid films rupture through spreading or bridging action, so as to achieve the effect of defoaming.