Emulsifier is a kind of substance that can make a mixture of two or more immiscible components form a stable emulsion.Its action principle is in the process of emulsion, the dispersed phase in the form of droplets (microns) dispersed in the continuous phase, it reduces the interfacial tension of each component in the mixed system, and the droplet surface to form a solid film or due to the charge of emulsifier is given in the droplet surface formation of electric double layer, prevent droplets gather each other, and to maintain uniform emulsion.From a phase point of view, the emulsion is still heterogeneous.The dispersed phase in the emulsion can be water phase or oil phase, most of which are oil phase.The continuous phase can be either oil or water, and most of them are water.An emulsifier is a surfactant with a hydrophilic group and a lipophilic group in the molecule.In order to express the hydrophilic or lipophilic properties of emulsifier, “hydrophilic lipophilic equilibrium value (HLB value)” is usually used. The lower the HLB value, the stronger the lipophilic properties of emulsifier.On the contrary, the higher the HLB value, the stronger the hydrophilicity.Various emulsifiers have different HLB values. In order to obtain stable emulsions, appropriate emulsifiers must be selected.