The absorbance, fluorescence and Scatchard plots methods as well as the effect of phosphate group on the fluorescence intensity of the cordycepin-DNA-EB system were used to study the interaction of the antitumor compound cordycepin and DNA. It is obvious tiat there is hyperchromic effect and hypochromic effect with slight red shift on the subtracted UV spectrum. It proves that the adenine base of cordycepin can be inserted into the double-helix of DNA. The results of the fluorescence intensity that decreases after increases with a little blue shift on the fluorescence spectrum also proved this. At the same time the phosphate can affect the cordycepin-DNA-EB system. Finally that the result depended on the Scatchard equation indicates that cordycepin reacts electrostatically on phosphate backbone of DNA. There also exists an intercalation into the double-helix of DNA.