Acoustic emission(AE) online monitoring test on corrosion in reinforced concrete specimens was launched. The aim of test was to study the relationship between acoustic emission signals and the actual location and extent of corrosion. The results show that the location figures of acoustic emission are in good agreement with the distribution of actual corrosion, and the same is true of the number of events of acoustic emission with the actual extent of corrosion. These results show it is feasible to monitor the entire process of corrosion with technology of AE, and the acoustic emission signals can effectively reflect the distribution and extent of corrosion.