The representative defoaming mechanisms of polysiloxane mainly include the "bridging-spreading" mechanism, the "bridging-dehumidifying" mechanism, and the "spreading-liquid entrainment" mechanism. The mechanism of "bridging-spreading" mainly starts from the basic point of "polysiloxane itself has relatively low tension and is easy to spread on the liquid film". It emphasizes that the defoamer droplets are easily deformed, but this theory cannot explain Differences in defoaming between polysiloxane alone and a mixture of polysiloxane and solid ions as defoamer. The mechanism of "bridging-dehumidification" is mainly from the point of view of the hydrophobicity of polysiloxane itself, but the defoaming effect of polysiloxane with high viscosity cannot be well explained. The "spread-liquid entrainment" mechanism has not been proven, because some facts indicate that the polysiloxane sometimes does not spread on the surface of the bubble film, but can also break the bubble.