In order to explore the property and mechanism of DNA condensation, the authors studies the effect of different concentrations of spermine(SPM), spermidine (SPD) and hexamminecobalt(III) chloride on the ultraviolet (UV) absorption value of calf thymus DNA by UV spectrophotometer from the macro. The results showed that SPD and SPM interaction with the DNA had the similar characteristics in UV spectrum. The UV absorption value of calf thymus DNA at 260 nm appeared increased-decreased-increased with the increasing the concentration of SPD and SPM. The value of hexamminecobalt(III) chloride system showed decreased and then increased, suggesting that SPM, SPD and hexamminecobalt(III) chloride could make DNA condense, but in different ways. Relatively, hexamminecobalt(III) chloride was more sensitive than SPD and SPM. The result of UV spectral analysis coincided with recent single-molecule experimental results.