Objective： The structure-activity relationship of longan polysaccharides and oat polysaccharides was preliminarily analyzed to provide scientific basis for the development of healthy food using longan and oat as raw materials. Method： Longan polysaccharides and oat polysaccharides were obtained from dried longan and oat bran by hot water extraction and deproteinization. The viable bacteria number and pH value were determined by adding two kinds of polysaccharides as carbon source and carbon-free MRS medium respectively， and the difference of beneficial effect was compared. Content and protein content were determined by gel permeation chromatography （GPC）. The monosaccharide composition was determined by GC/MS area normalization method. Amino acid composition was determined by HPLC-FLD method. The apparent morphology was observed by scanning electron microscope， rheology was measured by rheometer， and the structural basis of two kinds of polysaccharides were analyzed. Result： LP and OP as the sole carbon source could promote the proliferation of Lactobacillus casei， Lactobacillus acidophilus， Lactobacillus plantarum subsp. plantarum and Streptococcus faecalis， but proliferative effect of LP and OP were different. LP had a significantly better proliferative effect on Lactobacillus casei and Lactobacillus acidophilus subspecies than inulin（P<0.05）. The proliferative effect on Lactobacillus plantarum and Enterococcus faecalis was similar to inulin. OP had similar proliferative effect on Lactobacillus casei， Lactobacillus plantarum subspecies and Enterococcus faecalis. The effect was slightly higher than that of the blank group. The total sugar content of polysaccharide and oat polysaccharide was 61.2% and 68.3% respectively. The content of uronic acid was 10.1% and 5.9%， the content of reducing sugar was 16%， 5.4%， protein content was 2.2% and 2.9%. The average molecular weights（Mw） of LP and OP were 6.38×106 u， 5.42×103 u and 2.45×106 u， respectively. Longan polysaccharides consist of glucose， mannose， arabinose and so on. Oat polysaccharides mainly consist of glucose. The total amount and composition of hydrolyzed amino acids of the two polysaccharides are not significantly different. Scanning electron microscopy showed that the two kinds of polysaccharides were irregular sheets， the longan polysaccharides were smooth and tightly arranged， and the oat polysaccharides were rough and loosely arranged. In addition， the viscosity of the two kinds of polysaccharides solution was mass fraction-dependent， the viscosity decreases with the increase of temperature， and the viscosity of oat polysaccharides solution is more sensitive to temperature change. Conclusion： Longan polysaccharide had obvious proliferative effect on probiotics because of its complex monosaccharide composition， complex polysaccharide composition and low viscosity.