Abstract: Compared with single heat source, laser-TIG hybrid welding with the characteristic of optimum- designed heat source energy density and thermal-mechanical coupling mode is put to achieve precise forming and excellent properties in high-end equipment welding. This paper focuses on realizing high quality fusion welding of magnesium alloy to steel with Cu-Zn interlayer by utilizing the gradient energy density characteristic of laser-TIG heat source. The new idea of multicomponent liquid phase coexistence is put forward in welding magnesium to steel by hybrid laser-TIG welding, meanwhile the effect of Al element is analysed in the welding.