The invention relates to a device for measuring the thermal conductivity of vacuum glass, which comprises a support, a hot plate is arranged on the left side of the support, and a cold plate is arranged above the hot plate. The cold plate is communicated with a cooling water hose, the upper part of the cold plate is connected with an electric wheel by winding around a movable pulley of a vertical lifting limit switch on a cross beam via three soft ropes, the vertical displacement of the cold plate is also limited and coiled by a falling limit switch and a control device, and the hot and cold plates are ensured to stay in horizontal position state. The hot and cold plates can be ensured to stay in horizontal state by adjusting the length of the three soft ropes. Once the hot plate is in contact with the upper surface of the vacuum glass, the three soft ropes are in idle state, so that the pressure drop of the vertical lifting limit switch with the movable pulley almost becomes zero, and a power circuit of a motor is automatically cut off to stop falling. In addition, a level gauge automatically provides a signal about whether the cold plate stays in horizontal state before normal detection. The device has the characteristics of constant pressure in detection, good and uniform contact and accurate detection data.