The invention discloses sultam compounds shown in the formula 7, 8 or 9, wherein R1 and R2 are hydrogen or low-grade alkyl independently; R3 is methyl, ethyl, propyl, isopropyl, tertiary butyl or benzyl; R4 is hydrogen or halogen; and the halogen is preferably selected from fluorin, chlorine, bromine or iodine. The invention further discloses a preparation method of the sultam compounds, which comprises the steps of: restoring, esterifying and chloridizing N-butylcarbonyl fluoride-glutamic acid-5-benzyl ester (compound 10) to prepare sulfonyl chloride; performing deprotection ring closure to obtain sultam-gamma-carboxylic acid; and further deriving to obtain various gamma-substituted sultam compounds. The invention further discloses a midbody compound of the sultam compounds. The preparation method is simple in operation, high in product yield, high in purity, and easy in industrial production.