The representative polysiloxane defoaming mechanism mainly includes "bridging-spreading" mechanism, "bridging-dehumidifying" mechanism, "spreading-liquid entrainment" mechanism and so on. The "bridging-spreading" mechanism mainly starts from the basic point of "polysiloxane itself has a 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 be explained. Difference in defoaming between polysiloxane alone and a mixture of polysiloxane and solid ions as antifoaming agent. The mechanism of "bridging-dehumidification" is mainly from the perspective of the hydrophobicity of polysiloxane itself, but the defoaming effect of polysiloxane with high viscosity cannot be explained very well. The mechanism of "spreading-liquid entrainment" has not yet been proven, because some facts indicate that polysiloxane sometimes does not spread on the surface of the bubble film, but it can also break the bubble.