A new type of atomic force microscope(AFM) in liquid was developed.This article briefly discusses the principle and structure of this AFM,and introduces its unique characteristic.The applications of the AFM in the research of metal corrosion are reparted in detail.By using the AFM,the corrosion processes of carbon steel in sodium chloride solution and Pb in oxalic acid could be observed and the on-spot images of the sample surface were successfully gained.The results indicate that although it often has macroscopic consequences,the metal corrosion typically begins at the atomic or near atomic level,and then it proceeds through a pitting mechanism and through an apparent step dissolution process within terraces as well as at step sites and defects.