Abstract: Flavonoids often improve their biological activity after having coordinated with metal ions. In this paper, the coordination ratio of the complex of neohesperidin dihydrochalcone(NHDC) with copper(II) was studied by the method of molar ratio and continuous coordination in equal molar solution. Before and after the coordination, the complex structure was studied by UV, IR and X-ray diffraction. DPPH method, salicylic acid method and FRAP method were used to compare the variation of antioxidant activity. Results indicated that the coordination ratio of NHDC to copper was 2: 1, the stability of the NHDC-Cu (Ⅱ) complex was greatly affected by pH and the most stable state was at pH 7.0. The hydroxyl radical-scavenging activity was significantly enhanced possibly due to the improvement of water solubility and the increase of the amorphous degree after coordination with copper. And the increase of water solubility and bioavailability after NHDC coordination was attributed to the "concentrated effect" of copper on NHDC non-sugar ligand and the "embedding effect" of sugar part on the non-sugar part after NHDC coordination. However, there was no significant changes for scavenging fat-soluble free radicals like DPPH· and total reduction force by NHDC or its complex with Cu2+.