The invention provides application of a triterpenoid saponin compound in the preparation of medicaments for treating autoimmune diseases, in particular to application of a triterpenoid saponin compound in the preparation of medicaments for treating transplanting rejection, bronchial asthma, hepatitis B virus (HBV), nephrotic syndrome, yin-deficiency in hyperthyreosis or systemic lupus erythematosus. The triterpenoid saponin compound is shown by a chemical general formula as below, wherein in the chemical general formula, any two of R1, R2 and R3 are methyl, and the left one is a hydrogen atom R4 is pentahydric or hexahydric monosaccharide, or disaccharide formed by the pentahydric or hexahydric monosaccharide, or glycosyl formed by aldehyde acid derivatives of the monosaccharide or the disaccharide and R5 is the hydrogen atom or the pentahydric or hexahydric monosaccharide or the disaccharide formed by the pentahydric or hexahydric monosaccharide or a substituent group formed by thealdehyde acid derivatives of the monosaccharide or the disaccharide. According to the application, the medicaments for treating the autoimmune diseases obviously are provided.
