Eddy current testing instrument is the core equipment for non-destructive testing of key components in nuclear power plants, its performance is of great significance to ensure the safety of nuclear power units throughout their life cycle. At present, mainstream eddy current instruments use analog circuits for signal processing on the hardware architecture. The circuit structure is complex, and there are disadvantages such as high power consumption, high noise, and weak anti-interference ability. In order to solve the above problems and further improve the reliability of eddy current instruments, this paper creatively proposes a digital eddy current instrument architecture.In this architecture, ARM+FPGA is used as the core of signal processing, and DFT(Discrete Fourier transform) digital signal processing algorithms are used instead of traditional hardware detection circuits to complete the analysis of eddy current signals. The parallel DFT operation is realized in the algorithm, and up to 10 superimposed signals of different frequencies can be analyzed at the same time, which further improves the detection efficiency of the eddy current instrument.The test results show that the digital eddy current instrument designed in this paper greatly simplifies the hardware circuit, reduces the overall electronic noise level, reduces the power consumption, and improves the signal-to-noise ratio, stability and detection efficiency of the instrument. At the same time, the instrument supports BOBBIN, MRPC and ARRAY inspection technology, which can meet the NDT application needs of critical components in nuclear power plants.