Abstract: To solve the problem of testing the corrosion of the steel component with coatings, a pulse eddy current testing system is developed. The system composition parts, which include the sensors, the host and the software, are described in detail. The laboratory experiment and field application indicate that the system is able to detect the 10% wall thickness variation due to the corrosion when the coating thickness is 120 mm. The experimental result also shows the system can detect the steel corrosion with Aluminum and stainless steel sheet. Therefore, an online testing method is proposed.