NOVELTY - The diesel composition comprises base diesel and additive, where the base diesel contains biodiesel; the additive contains constituent a; and the constituent a is polymer of amide containing one or more of unsaturated binary carboxylic acid, anhydride, monoester and diester. The content of the additive is 100-8000 ppm. The number-average molar mass of the constituent a is 1000-50000. The constituent a is prepared by condensing monomer A and monomer B polymerized and ammonia and/or organic amine containing ammonia functional group.    USE - Used as a diesel composition.    ADVANTAGE - The diesel composition is safe and eco-friendly manner, and has better stability.    DETAILED DESCRIPTION - The diesel composition comprises base diesel and additive, where the base diesel contains biodiesel; the additive contains constituent a; and the constituent a is polymer of amide containing one or more of unsaturated binary carboxylic acid, anhydride, monoester and diester. The content of the additive is 100-8000 ppm. The number-average molar mass of the constituent a is 1000-50000. The constituent a is prepared by condensing monomer A and monomer B polymerized and ammonia and/or organic amine containing ammonia functional group, where the monomer A is one or more of unsaturated dicarboxylic acid and anhydride, mono-ester and diester; and the monomer B is the monomer containing alkenyl different from the monomer A. The mole ratio of the monomer A to the monomer B is 1:0.1-10. The number-average molar mass of the polymerized product is 100-50000. The number of the carbon atom of the monomer A is 4-10. The monomer B is olefin, olefin acid ester, and enol ester, where the carbon atom number of monomer B is 2-30. The monomer A is maleic acid, maleic anhydride, maleic acid monoester, fumaric acid, fumaric acid monoester. The monomer B is alpha -cetene, alpha -octadecene, (methyl) acrylic ester, vinylacetate and propenyl ester. The polymerization is processed in existence of solvent and initiator. The polymerization condition comprises temperature of 40-250 degrees C for 1-10 hours. The mole ratio of the monomer A to the ammonia and/or organic amine is 1:0.5-5. The additive further contains constituent b and constituent c, where the constituent b is aromatic amine antioxidant and/or blocked phenolic antioxidant, the mass ratio of the constituent b to the constituent c is 0.01-10:1, constituent c is metal passivator, and the weight ratio of the constituent a to the constituent c is 1:0.01-1. The constituent is p-phenylenediamine derivant antioxidant, and blocked phenolic antioxidant of which at least one tertiary butyl is at o-position of phenolic hydroxyl. The constituent b is dialkyl p-phenylenediamine with the carbon atom number of 4-10 and bisphenol antioxidant connected by methylene or sulfur. The constituent b is N,N-heptyl p-phenylenediamine, N,N-di sec-butyl p-phenylenediamine, N,N dioctyl p-phenylenediamine, N,N-bi-(1- methyl heptyl) p-phenylenediamine, 2,2- methylene-bis(4-methyl-6-tert butylphenol), 4,4-methylene-bis(2-methyl-6-tert-butylphenol), 4,4-methylenebis(2,6-tert-butylphenol), 4,4-methylenebis(2-tert-butylphenol), 4,4-sulfo-bi(2-methyl-6-tert-butylphenol), 2,2- sulfobi(4-methyl-6-tert-butylphenol), 4,4-sulfo-bi(2-methyl-6-tert-butylphenol), 4,4- sulfo-bi(2,6-di-tert-butylphenol), and bi-(3,5-di-tert-butyl-4-hydroxybenzyl) sulfur ether. The constituent c is ammonium salt formed by triazole and fatty amine, triazole, formaldehyde and fatty amine by Mannich reaction, Schiff base and organic polycarboxylic acid. The base diesel further contains other diesel. The other diesel is petroleum diesel oil, Fischer-Tropsch synthesis diesel, hydrocracking biodiesel, and diesel concoction containing oxygen and the volume ratio of the biodiesel to the other diesel is 1:0-99. An INDEPENDENT CLAIM is included for a method for improving oxidation stability of biodiesel.