Abstract: “Insulator-conductor” composite structures are widely used in various fields and in view of the testing needs of these structures, a dual-mode non-destructive testing system based on phase switching between capacitive and inductive modes was developed. The characteristics of the detection field of the planar coil sensor were analysed by using the finite element simulation model, and the feasibility of the dual-modality sensor for defect detection of conductor and insulator samples was verified. The signal processing circuit was designed according to the characteristics of the detected signals in the two modalities, and the hardware circuit switching was realized through a multiplexing structure. The software of the detection system was developed, which realized the program control mode and the acquisition and analysis of the data. The hardware and the software systems were integrated with the MCU main control circuit as the core, thereby forming the dual modality detection system. The scanning experiments of the composite structure samples were designed to verify the detection performance of the system.