The diffuse-reflectance FTIR spectroscopy (DRIFTS) and attenuated total reflection FTIR (ATR-FTIR) were used to study polygonum multiflorum Thumb and its extracts. The result shows that when acetone is used as extraction agent, the contents of extracts in polygonum multiflorum Thunb’s phloem are highest, those in polygonum multiflorum Thunb’s xylem are the lowest. Compared with DRIFTS and ATR-FTIR, it can be found that there are some differences between polygonum multiflorum Thunb and its extracts. There are two gentle absorption peaks at 3 576 and 3 147 cm-1 respectively for polygonum multiflorum Thunb, while there is a strong absorption peak at 3 351 cm-1 for its extracts, showing that there may be more OH… active ingredients in polygonum multiflorum Thunb’s extracts. Meanwhile, polygonum multiflorum Thunb has strong absorption peaks at 931, 859, 766 and 709 cm-1 respectively, while its extracts have no resembling absorption peaks. It also shows that the extracts are active ingredients.