This paper investigates the corrosion behavior of 2205 duplex stainless steel in 0.1%、1.0% and 3.5% NaCl solution by electrochemical measurements. The experimental analysis based on PDM (Point Defect Model) shows that the pitting corrosion resistance of the material tends to be worse with the increasing of concentration of NaCl solution. Because when the passive film forms, oxygen ion vacancy is produced on metal/film interface and consumed on film/solution interface, but metal ion vacancy exists on film/solution interface and consumes on metal/film interface. Migration of oxygen ion vacancy causes growth of the passive film but it also destroys the film simultaneously. In addition, on the basis of PDM theory, a dissolution model of passive film has been established. The model explains that the passive film of 2205DSS on austeniteγphase probably dissolves faster than on ferriteαphase in the simulated marine environment.