Abstract: Based on the general principles of chemistry, physical-chemistry and crystallography, the welding metallurgical physical-chemical properties of low hydrogen basic electrodes are investigated in this paper, including such topics as the dehydrogenation by calcium fluoride, the balance amount of calcium fluoride in the slag, the influence of calcium fluoride content in electrode coating on fumes and toxicity, the suppression of the volatilization of NaF and hence the decrease in toxicity by the formation of the almost non-volatile and insoluble chemical compound NaF-MgF₂, etc. The soluble fluorides formed in small amounts by the interaction of coating materials in electrode making are also studied. The form of manganese existing in the fume is determined by analysis. A new low fume and low toxicity CaO-SiO₂-TiO₂-CaF₂ type coated basic electrode with better welding characteristics is developed, complying with the hygiene and the mechanical property specifications of our national standards.