Abstract: The wheel cylinder is the important security part in a car. For quality control of bore surface of wheel cylinder, the method of eddy current testing with revolving probe was proposed. The paper designed a semiautomatic eddy current testing system with revolving probe for bore surface defects of wheel cylinder. The paper described the eddy current probe, mechanical transmission and control device. The practical application in DELPHI indicated that the system could detect a 0.5 mm hole of bore surface. Signal noise ratio was higher than 8 dB. Testing speed was four per minute. The result indicated that system could meet the demand of quality testing of wheel cylinder. The system could be used for testing surface detects of other parts in the car also.