The invention discloses a preparation method of multifunctional oxyamide for an oil field and an application thereof. Long-chain fatty acid amide is prepared by taking natural oil as a raw material, and then oxyamide is prepared through an addition reaction by taking an aldehyde compound as a hydroxylation reagent. The oxyamide is used as a crude oil additive, so that the viscosity and condensation point of the crude oil can be reduced; meanwhile, through the coordination of nitrogen and oxygen atoms with metal, the oxyamide is adsorbed to the metal surface and forms an organic protection layer to realize a corrosion inhibition effect.