A common and urgent problem in electric vehicle wireless charging technology is the accidental entry of metal objects into the charging area where there is no direct physical contact. Eddy currents can be induced in the metal objects, generating a large amount of heat and potentially leading to serious consequences such as fire. The current commercially applied metal object detection technology has the problems of low detection sensitivity, affecting the power transmission magnetic field, and the existence of blind zones. In view of these shortcomings, a metal object detection system for wireless charging of electric vehicles is proposed in this paper. Long strip detection coils are designed and placed above the transmitter coil. Each strip detection coil is composed of 16 unipolar coils having alternating polarities, which can realize decoupling between the detection coil and the transmitter coil and eliminate the interference to the magnetic field of the wireless power transmission system. A third-order Sallen-Key high pass filter and a proportional amplifier circuit are used to improve the sensitivity and accuracy of metal object detection. Finally, an experimental platform of metal object detection for electric vehicle wireless charging is built, and the proposed system can detect the existence of metal objects sensitively and accurately at the location where they may exist.