The invention provides a nickel-nickel oxide-magnesium oxide composite negative electrode for enhancing strength of atmospheric pressure discharge plasma and a preparation method and application of the composite negative electrode. By the nickel-nickel oxide-magnesium oxide composite negative electrode, the number of seed electrons released by the negative electrode is increased, and the strength of the discharge plasma is further enhanced. The nickel-nickel oxide-magnesium oxide composite negative electrode sequentially comprises metal nickel, an intermediate nickel oxide layer and a magnesium oxide layer from bottom to top, wherein the magnesium oxide layer with 20-50 micrometers is coated on a surface of the metal nickel, and the compact nickel oxide layer is grown between the metal nickel and the magnesium oxide layer by high-temperature calculation so as to form a composite structure of the metal layer, the intermediate nickel oxide layer and the magnesium oxide layer. A magnesium oxide and nickel oxide insulation layer in the composite structure has an effect of charge accumulation during the whole discharge process, a strong electric field higher than 106V/cm is formed between the coating layer and the metal surface, and metal nickel electrons are induced to move out of and penetrate out of the magnesium oxide layer to be used as seed electrons due to a tunnel effect. The nickel-nickel oxide-magnesium oxide composite negative electrode provides references for application of the atmospheric pressure discharge plasma in fields such as chemical industry, materials, biology and environmental friendliness.