Abstract: Pure zinc sacrificial anodes didn't play a role in a heat transfer tube syetem. The failure reason of sacrificial anodes was analyzed by means of appearance analysis, microstructure study and electrochemical methods. The results showed that there was 1-2 mm non-metalline sediments on the sacrificial anode surface, the main composition of the semdiment was basic zinc chloride which made the surface of sarcrifical anode insulated. It was found that there was a large amount of iron rich precipitates in the microstructure of sacrificial anode, which is not in conformity with the high purity zinc standard. The self-corrosion of the sacrificial anode was detected in a short run, and the surface deposit of the sacrificial anode was rapidly generated. The contents of iron, copper, lead and other harmful elements in the anode were overweighted seriously which led to the formation of harmful second phase, and the self-corrosion was easy to produce in sacrificial anode, resulting in the formation of surface sediments.