Eddy current testing employs rich frequency sinusoidal signal as the excitation source, and many frequency components are included in corresponding response. Meanwhile, the counter-interference of eddy current testing is improved. An eddy current testing system suitable for on-line detection is developed based on current testing, data acquisition and virtual instrument. The system was composed of eddy current testing hardware circuit, PXI bus system and relative software. The hardware circuit generates excitation signals with excellent waveform, stable frequency (range of 0~5MHz) and stable amplitude. Combining with PXI bus system and LabVIEW virtual instrument software platform, the system offers functions of acquisition, analysis, processing and display of the signals. Testing experiments were done through the system, and the results showed that the system can detect the defect diameter of 0.6mm, with a good testing capability.