The invention relates to rhubarb polysaccharides, wherein the rhubarb polysaccharides comprises rhubarb polysaccharides with the range of molecular weight section of between 0.2 and 0.3x10<5> and between 1 and 1.2x10 <5>. The rhubarb polysaccharides are prepared from the traditional Chinese medicine of rhubarb by the processes of ultrasonic extraction, ultrafiltration separation concentration, and purification. The rhubarb polysaccharides can be made into a rhubarb polysaccharides medicine composition together with a medically acceptable carrier. The medicament type which can be made into comprises freeze-dried powder injection, powder-injection, injection solution, orally disintegrating tablets, dispersible tablets, effervescent tablets, controlled release tablets, sustained-release tablets, common film-coated tablets, capsule, granular formulation, dropping pills, and the like. The rhubarb polysaccharides medicine composition is used for treating diabetes, resisting tumor, resisting aging and improving the immunity.