Abstract: Aimed at the corrosion feature of the air cooler fin tube for high pressure hydrogenation refining, the defects of the air cooler fin tube in service can be accurately detected by the remote field eddy current testing technique combined with the normal eddy current one. The article mainly described the detecting method of the air cooler fin tube in service and our detecting results were compared with those from dissection. The results showed the said detecting method was of comparatively higher accuracy and reliability. It was concluded that the air cooler fin tube’s corrosion could be accurately detected by the remote field eddy current testing technique combined with the normal eddy current testing.