Abstract: Water absorption amount and corrosion resistance of epoxy powder coating on surface of Q235 steel in NaCl solution of different contents (mass fractions of NaCl in solution were 0, 1.0%, 3.5%, 6.0%, 8.5%) were studied by weight gain method and electrochemical method. The effect of chloride ion on the failure of the coating was analyzed. The results show that with increasing content of chloride ion in the solution, the saturated water absorption amount decreased, and the time interval for reaching the saturated water abroption was shortened. The chloride ion accelerated the failure of the epoxy powder coating. Moreover, the higher the chloride ion content in the solution was, the faster the coating failed, the earlier the interface corrosion occurred, and the more severe the corrosion of the metal matrix was.