Multi-layer metal plate structure is an important load-bearing component of aircraft, which has the characteristics of large thickness and complex structure. The structure is easy to produce defects in service. Remote field eddy current technique (RFECT) can penetrate the tested component with large thickness. RFECT has the ability of detecting hidden defects with large buried depth. However, the traditional RFECT is limited by the structure of the sensor, which is commonly used in the detection of pipeline defects. In this paper, a plane remote field eddy current technique (PRFECT) sensor that adopts a new structure of coaxial placement of sensing coil and excitation coil is designed by simulation software ANSYS. The new PRFECT sensor can detect deeply buried defects in multi-layer plate structures with higher sensitivity. The influence law of defect size and buried depth on detection signals are obtained by simulation. Both simulation and test results prove the feasibility of the new structural PRFECT sensor for detecting hidden defects in multi-layer plate structure.