Abstract:A plain high-current diode is fielded on the “Jianguang-I” accelerator preline, and the diode resistance is theoretically estimated. Impedance measurement experiment is conducted, and the experimental results are analyzed combined with the electron beam density gained by a small Faraday cup array and Particle in Cell(PIC) simulation. The results show that there is a high correlation among the impedance value of the diode, the impedance curve, the Faraday cup waveforms and the beam pinching level. When the impedance curve is at the front (where impedance is established) or at the end (impedance collapsing), the beam is in the non-pinching period, the Faraday cup signal has no valid data. When the impedance curve is in the flat area, the diode works well and the beam pinching and Faraday cup signal are stable, and the Faraday cup waveform at the anode edge shows double peaks, which is consistent with the beam pinch motion.