Abstract: Poly L-cysteine modified electrode was prepared by cyclic voltammetry method,with which the interaction between dopamine (DA) and herring sperm DNA with the presence of copper ion in the Tris-maleic acid buffer solution was studied.Result showed that there was an obvious redox peak of DA on the poly L-cysteine composite film modified electrode in the Tris- maleic acid buffer solution of pH7.0.After adding the DNA,the redox peak decreased obviously.This suggested that there was an interaction of DNA and DA.The redox peak of DA decreased further as adding copper ion,which showed that copper ion had great effect on the interaction of DA and DNA.