OBJECTIVE To investigate the mechanism of electrothrombosis by copper needle, in order to supply the referential data for clinical treatment of vessel deformity. METHODS The mechanism and condition of thrombus formation by copper needle were studied in vivo and in vitro using electrophysics, atom absorption spectrophtometry, histological, and histochemical methods. RESULTS Great deal of copper ion was dissociated, and agglutination of red blood cells(RBC) in blood could be observed in vitro after the current applied by copper needles. Formation of stable thrombus was related to voltage and time of application of electric current. CONCLUSION Dissociation of copper ion and agglutination of RBC are the basic principle of electrothrombosis with copper needle. A 4V direct current and 17.5 minutes are the safe and effective conditions for thrombus formation in the blood vessels.