The invention provides a composite 
corrosion inhibitor 
electrolyte, an application thereof and a 
magnesium air battery, and belongs to the field of air batteries. In the invention, La<3+> in lanthanumnitrate can react with OH<-> in the solution to generate 
lanthanum hydroxide to precipitate, and the structure and appearance of a passive film are changed, so that 
hydrogen evolution is inhibited, the damage effect of 
nitrate ions on the passive film is weak, and the integrity of the primary passive film is ensured, thereby having a good protection effect on internal battery materials, and inhibiting the 
hydrogen evolution. CTAB is a cationic surfactant, can significantly reduce the 
surface tension, change the surface state of 
metal / 
electrolyte, gather on the surface of active 
metal by utilizing the 
electrostatic adsorption of NH<2+>, reduce the 
surface energy of the 
metal and increase the 
corrosion activation energy, thereby slowing down the 
corrosion rate, and simultaneously forming alayer of hydrophobic protection film on the 
surface layer of the metal, thus hindering the charge and 
ion transfer, hindering the reaction process and reducing the corrosion rate.