The bronze cultural relics had been badly corroded by soil, water and chloride after lying underground for thousands of years and the bronze corrosion its easily spreading. Study on the phenomenon showing that, the bronze corrosion can be divided into two kinds, one is cause by oxygen or sulfur, which is steady and colorful. The other is caused by chloride, which is corrosion – spreading and entering deeply into the bronze body. This is called barmful rust and should be got rid of. Protection agent for harmful erosion conversion is studied and produced. It can convert the harmful rust to harmless, and then the relics can be preserved by coated with a protecting film. This method had been used on the Western zhou bottle and Sui Dynasty mirror, which were exhibited on Guangzhou Shekou Museum. At the beginning, they were badly corroded and in a powdery state. After protection process and stored in ordinary warehouse for 4 years, they are in good state, free of rust spot. This method also used on 49 Western Han Wuzhu Coins, which were powdery corroded, after 7 years in the air, the coins are good and free of rust spots. Reversibility test, acid resistant test, alkali resistant test, salt resistant test and harmful rust remove test are also made, showing the effectiveness of this agent. The agent consists of composite corrosion inhibitor, coupler and adhesive. It can combine with Cu+ to form stable coordinated compound. When removing the harmful rust, it did not change the appearance of the protected objects. So the rust is removed and relics be protected simultaneously. The traditional techniques of mechanics and chemistry no longer needed.