The interaction atrazine and ct-DNA was studied using fluorescence probe and UV absorption spectroscopy technique. Ethidium bromide (EB) was used as a probe. The effects of atrazine, phosphate, concentration of ions, and potassium iodide on the fluorescence of ct-DNA-EB system were investigated. The results showed that the fluorescence quenching process of atrazine to ct-DNA-EB system was proved to be the simultaneous dynamic and static quenching model. The phenomena of fluorescence quenching of ct-DNA-atrazine system by KI and hyperchromicity and the red shift of DNA UV-absorption caused by atrazine indicated the existence of intercalation between atrazine and ct-DNA. The experiments of phosphate and ionic strength showed that atrazine could combine with the phosphate group of ct-DNA by non-characteristic static force, and this action could be inhibited by high ionic strength.