Abstract: Effects of the tip end thickness of ZrO₂(MgO) tube and the amount of reference electrode addition on the response time were investigated in this paper. It is concluded that the optimized parameters for tip thickness of ZrO₂ (MgO) tube and the amount of reference electrode are 0.60~0.80mm and 40~60mg respectively. The thermal equilibrium of response process for oxygen probe using "Two TC Method" was also investigated. The results show that the heat transfer in the oxygen galvanic cell is the limitting-step in the response process and the peak appeared in the EMF curve is resulted from the thermal equilibrium in the oxygen galvanic cell.