The failure process of fluorocarbon coating in 3.5% NaCl solution under wet-dry cyclic condition was studied with electrochemical impedance technique，Fourier transform infrared spectrometry(FTIR)and scanning electronic microscope(SEM).The results showed that the failure rate of coating under wet-dry environment was faster than that under complete immersion condition. The wet-dry condition promoted formation of micro-pores in the coating and resulted in decreased coating resistance and increased water absorption. The failure mechanism for fluorocarbon coating under wet-dry environment was suggested. The coating volume experienced swelling and contraction during the wet-dry cycle，which resulted in increased micro-pores and cracks in the coating. Electrolyte entered the coating defects under the action of osmotic pressure，leading to blisters and reduced adhesion of the coating to the substrate.