Objective: The structure of CLPS1 (polysaccharide fraction 1 of Codonopsis lanceolata) was determined to provide a basis for the study of polysaccharide activity of C. lanceolata and the development of natural plant polysaccharides. Methods: After extraction, separation, and purification, the separation component CLPS1 was determined by gas chromatography, infrared spectroscopy, nuclear magnetic resonance, periodate oxidation, Smith degradation, and methylation analysis to determine the structure of CLPS1. Results: The specific rotation of CLPS1 is +44°, the content of the total polysaccharide is 97.6%, the uronic acid of CLPS1 is 13.18%, and the molecular weight of CLPS1 is 91.7. The monosaccharide component of CLPS1 contains Ara, Gal, Glc, GalA, The molar ratio is 2.7∶3.4∶2.3∶1.1∶0.5. Chemical composition and structure of polysaccharide CLPS1 was studied by infrared spectrum, NMR, partial hydrolysis with acid degradation, Smith, methylation and GC-MS. The results showed that monosaccharide compositions of CLPS1 contained GluA and pyranose, while pyranose included both α-pyranoside and β-pyranoside in structure. The backbone was composed of Ara and Gal, the brancd with Gal and the terminal residues of backbone with Glu. Branch point of Gal residues is linked by Glc (1→4，6); Gal (1→3，6); Gal contains 1→,1→3,1→4,1→6,1→3,6; Gal contains 1→, 1→3, 1→4, 1→6, 1→3, 6; Glc contains 1→,1→4,1→4,6; Ara contains 1→5; Galacturonic acid 1→3. Conclusion: CLPS1 is a complex acidic polysaccharide. The structure analysis of C. lanceolata polysaccharides is the basis for studying the structure-activity relationship of C. lanceolata polysaccharides, which is of great significance for understanding the biological activity and mechanism of C. lanceolata polysaccharides.