The choice of defoaming agent should accord with the following characteristics: 1, in the foaming liquid insoluble or insoluble burst foam, defoaming agent should be concentrated on the bubble film. For the situation of the defoamer, should be concentrated in an instant, concentration, for the bubble should often remain in this state. Therefore, the defoamer in the foaming liquid is supersaturated state, only insoluble or difficult to dissolve is easy to achieve supersaturated state. Insoluble or insoluble, it is easy to gather in the gas-liquid interface, it is easy to concentrate on the bubble film, it can play a role at a lower concentration. For defoamer used in water system, the molecule of active ingredient must be strong hydrophobic and weak hydrophilic, HLB value in the range of 1.5-3, the best effect. 2. The surface tension is lower than that of foaming liquid. Only when the intermolecular force of the defoamer is small and the surface tension is lower than that of the foaming liquid can the defoamer particles be immersed and extended on the bubble film. It is worth noting that the surface tension of the foaming solution is not the surface tension of the solution, but the surface tension of the foam solution. 3. It has a certain degree of affinity with foaming liquid. Since the defoaming process is actually a competition between foam collapse rate and foam formation rate, the defoaming agent must be able to disperse quickly in the foaming liquid in order to quickly play a role in a wider range of foaming liquid. In order to make the defoaming agent diffusion faster, the active components of defoaming agent must have a certain degree of affinity with foaming liquid. The active ingredient of antifoaming agent is too close to the foaming liquid and will dissolve. Too sparse and difficult to disperse. Only the appropriate affinity, the effectiveness will be good. 4. No chemical reaction occurs with foaming liquid. Defoaming agent and foaming liquid reaction, on the one hand defoaming agent will lose the effect, on the other hand may produce harmful substances, affect the growth of microorganisms. 5. Low volatility and long acting time.