Abstract: Molecular mass distribution of Astragalus polysaccharides is wide. Astragalus polysaccharides prepared by conventional water extraction and alcohol precipitation are mostly mixture of macromolecules. Although studies have shown that Astragalus polysaccharides have two-sided immunomodulation, the relationship between anti-inflammatory components and molecular mass distribution of Astragalus polysaccharides is not clear. Therefore, Astragalus polysaccharides were extracted by water extraction and alcohol precipitation. The relative molecular weight of them was determined by high performance gel permeation chromatography (HPGPC). Astragalus polysaccharides with different molecular weights were separated and prepared by membrane separation. RAW 264.7 cells were induced by lipopolysaccharide (LPS) to establish an inflammatory cell model in vitro and the anti-inflammatory polysaccharide were screened. The anti-inflammatory regulation mechanism of Astragalus polysaccharides was analyzed by the LC-MS/MS metabonomics technology. The results showed that APS was composed of APS-Ⅰ ( > 2 000 kDa) and APS-Ⅱ (10 kDa). APS-Ⅰ was composed of mannose, rhamnose, galacturonic acid, glucose, galactose, arabinose and the molar ratios of these monosaccharide of APS-I were 0.54∶0.26∶12.24∶17.24∶8.46∶1. APS-II was composed of rhamnose, galacturonic acid, glucose, galactose, arabinose and the molar ratios of these monosaccharide of APS-II were 0.26∶0.14∶24.04∶0.62∶1. APS-Ⅰ and APS-Ⅱ had no cell toxicity to RAW 264.7 macrophage in the range of 0-100 μg·mL^-1. Compared with the model group, APS-I at a concentration of 0-100 μg·mL^-1could significantly inhibit the secretion of NO and TNF-α by RAW 264.7, and can significantly promote the secretion of IL-10. APS-I had better anti-inflammatory activity than APS-II in vitro. The metabolomics results showed that 32 different metabolites were found between the model group and blank group; APS-I group can significantly callback 18 different metabolites; mainly related to arginine biosynthesis, arginine and proline metabolism, pyrimidine metabolism, citric acid cycle (TCA cycle), cysteine and methionine acid metabolism, tryptophan metabolism. This study found that APS-I had better anti-inflammatory activity than APS-II in vitro, and its mechanism may be closely related to amino acid metabolism and energy metabolism, which indicated the direction for further clarifying the pharmacodynamic material basis of Astragalus polysaccharides.