The raw material of this study was Chuanminshen violaceum from Three Gorges Reservoir， crude polysaccharide of C. violaceum was obtained by ultrasonic assisted water extraction and alcohol precipitation， its structure was characterized through ultra high performance liquid chromatography tandem mass spectrometry（UPLC-MS/MS）， high performance gel permeation chromatography（HPGPC）， ultraviolet visible spectrum（UV）， Fourier transform infrared spectrum （FT-IR） and nuclear magnetic resonance spectroscopy （NMR）. In addition， the antioxidant capacity of crude polysaccharide of C. violaceum was investigated by hydroxyl radical scavenging rate， iron ion chelate and ability and reduction power. The results showed that the crude polysaccharide of C. violaceum was a kind of proteoglycan with molecular weight of 11.7 ku and connected with protein through -O-. Its polysaccharide was mainly composed of rhamnose （1.24%）， galacturonic acid （1.81%）， ribose （3.47%）， galactose （8.42%）， mannose （17.67%）， arabinose/xylose （27.83%） and glucose（39.55%）. And through the α-1，4-glycosidic bond and a certain amount of α-1，2-glycosidic bond， α-1，6-glycosidic bond and α-1，5-glycosidic bond， and a very small amount of β-1，4-glycosidic bond and β-1，6-glycosidic bond to connect. Additionally， the antioxidant experiments of the crude polysaccharide showed that the crude polysaccharide had good antioxidant activity， and there was an obvious dose-effect relationship between its activity and concentration in the low concentration range.