1.Steady arc. Ensuring the stable combustion of welding arc and making the welding process stable is the necessary condition to ensure the welding quality. 2.Protection of arc and molten pool. Nitrogen, oxygen and other gases in the air are harmful to the metallurgical reaction of the welding pool. The gas produced by melting the electrode skin can isolate the air. Prevent harmful gas from invading the molten pool. The electrode melts and forms slag, covering the weld surface and protecting the weld which is not completely cooled. Reducing the cooling rate of the weld is beneficial to gas escaping. Prevent air blowholes. Improve the microstructure and properties of the weld. 3.The skin of the drug is involved in a complex metallurgical reaction. The required alloy elements are infiltrated into the weld metal through the skin of the drug, which can play a role in controlling the chemical composition of the weld, so as to obtain the required weld metal properties. Adding alloying elements such as silicon manganese in the skin of the electrode can be used to surmount the harmful gases and impurities, such as deoxy desulphurization and dephosphorization, and improve the quality and performance of the weld.