Abstract: In order to achieve pipeline eddy current inner inspection based on planar coil sensors, a L type planar coil sensor was designed and an experimental system for eddy current inspection was developed. The defects inspection capability of the eddy current sensors with different parameters was analyzed from both the amplitude and phase of the inspection signal. The experimental results showed that, in addition to the significant impact of lift-off, the thickness of the planar coil PCB board, the upper and lower positions of the excitation coil and the receiving coil had a significant impact on the inspection capability either. A PCB coil with a smaller thickness can achieve higher sensitivity. The configuration of an exciting coil located on the lower side near the tested pipeline and a receiving coil located on the upper side was also beneficial for improving inspection capability. The developed planar coil sensor can detect closed cracks and pinhole type of metal loss of 2 mm (length)×2 mm (width)×2 mm (depth).