The work aims to study the pitting corrosion causes and mechanism of 304 stainless steel in atmospheric envi-ronment of the south China sea. Potentiodynamic polarization, electrochemical impedance spectroscopy, scanning electron mi-croscopy and Kelvin probe technology were used to analyze and investigate 304 stainless steel exposed for different periods in the atmospheric environment of the south China sea. With the extension of exposure time, the number and depth of pitting pit on 304 stainless steel surface gradually increased, the passivation interval was shortened, the pitting potential moved negatively, the slope of the anode polarization curve was obviously reduced, and passivation phenomenon appeared repeatedly. Passivation curve gradually disappeared and the resistance of the membrane layer in the impedance test became smaller and smaller. SEM indicated that 304 stainless steel showed discontinuous pitting at early exposure, pitting pits developed deeper and deeper, and pitting groups appeared at late exposure. At local part, multiple pitting pits were linked together to form ulcer-like corrosion surfaces. With exposure time increased, the surface potential unevenness of Kelvin in the scanning sample was gradually enhanced. The corrosion resistance of 304 stainless steel samples decreases with the increase of exposure time and the pitting phenomena increases continuously. Pitting pits mainly develop in depth at the beginning of exposure. At the later stage of exposure, after the width of the pitting pit reaches a certain level, the bulk solution migrates into the pit and dilutes the acidity of the solution in the pit, so the pitting pit develops simultaneously in longitudinal and lateral direction.