Abstract: The existed some difficulty to test the turnout surface for a continuous variable cross-section. A kind card-type eddy current sensor was developed, suitable for testing the narrow space between the inner turnout surfaces. The sensor was comprised of an elastic metallic sheet, a plurality of detection coils, and a single thin magnet. It fits well with switch rail with two magnet sheet, to reduce the lift-off effect of the eddy current and the detection sensitivity was improved. The thickness of the sensor was 0.8 mm, especially for testing switch rail and the narrow space between the inner turnout surface defects. The testing results showed that the sensor fully met with the requirements of site testing switch rail.