Oil foaming can be divided into two aspects, one is surface foaming, usually can be controlled with anti-foaming agent; The other is the foam inside the oil, the internal foam is not easy to improve by anti-foaming agent, and the effective anti-foaming agent on the surface foam may make the oil internal foam more stable. For the need for excellent defoaming performance of the oil, it is necessary to choose the base oil and additives to be blended. The mechanism of action of antifoam agent is complicated, and there are different opinions. The representative views include reducing partial surface tension, expanding and penetrating. 1, to reduce the surface tension of the mechanism is realized by reducing the surface tension, this kind of view is that the surface tension of the antifoaming agent is smaller than foam fluid, when the antifoaming agent after contact with the membrane, reduce the surface tension of the bubble film local and the rest remains unchanged, strong bubble film tension pulling its weaker section, so that the bubble burst. However, this mechanism is limited to local locations, because these substances do not dissolve in water, so the diffusion force is poor, do not have much effect on the surrounding foam. When the local tension on the surface of the foam is reduced, under the action of this force, it slowly diffused to all sides and finally formed a burst. 2. Expansion This view holds that the anti-foaming agent droplets invade into the bubble membrane and make it a part of the membrane, and then expand on the membrane, which can effectively inhibit the diffusion of the active agent, making it difficult to exert its elastic ability, so as to eliminate the surface foam. 3. Penetration This view believes that the role of anti-foam agent is to increase the permeability of the bubble wall to air, thus accelerating the merger of foam, reducing the strength and elasticity of the bubble membrane wall, and achieving the purpose of bubble breaking.