The novel theory for microstructure control of magnesium-containing ternary alloy coatings was firstly put forward. It was pointed out that the factors which influence the microstructure of coatings were not only the composition, but also the solidification route. The solidification route could be optimized by adjusting the cooling rate during different cooling stages, so as to improve the product performance. With full consideration of the suface quality of coatings and the suppression of liquid metal alloy oxidation, three solidification routes for magnesium-containing coatings were scientifically planned. On the basis of comprehensive theoretical research and practical experience, the liquid cooling and solidification processes of the coatings were optimized. This novel theory guides the design of hot-dip coating process of magnesium-containing ternary alloy coating, as well as the development of key equipments and intelligent systems. It has been applied to practical engineering projects, and the corrosion resistance of the products has reached the international leading level.