Abstract: The reference electrode of Ag/AgCl packed in a mullite tube in the LiCl-KCl molten salt was fabricated. The resistances of the reference electrode separator at different temperatures were determined using LCR method. The stability, reproducibility and reversibility of the electrode were tested and effect of AgCl concentration on electrode stability was studied. The characterizations indicate that the component of reference electrode diaphragm is 3Al₂O₃•2SiO₂ with good ionic conductivity. The reference electrodes are stable in ±2 mV for about 40 h in the molten salt. Only ±5 mV change is found after 4-cycle usage. The open circuit potential can be recovered within 15 s after a treatment with ±5 mA polarization current for 5 s. The Ag/AgCl electrode packed by mullite tube shows excellent performance for the controlling of the electrode potential in LiCl-KCl molten salt.