For the need of modern industrial safety testing of surface and nearsurface defect detection of nonferromagnetic workpieces, based on the principle of eddy current testing and the giant magnetoresistive (GMR) sensors, Nondestructive Testing method is an effective eddy current testing technique which has a lot of advantages such as the high sensitivity, high resolution, wide operating frequency range (0Hz to MHz), small sensor volume and simple signal processing circuit and easy integration. In this paper, one simple and excellent GMRbased eddy current system is designed. The GMR sensor with high sensitivity of 30mv/Oe, the microcontroller STM32based direct digital synthesis signal generation method and phaselock technique are used in this system. The results show that the GMRbased eddy current system can detect the presence of the defective on the surface or under the aluminum plate surface 2 mm, the shape and location can be known by multichannel scanning. The system can accurately perform nondestructive testing of surface or nearsurface defect detection for nonmagnetic metals.