The utility model relates to a vacuum dew point monitoring devices, it includes constant voltage power supply, vacuum meter, dew point hygrometer, a time relay, the 2nd time relay, AC power output end is connected with a time relay, just a time relay, the 2nd time relay and vacuum meter are parallelly connected to be set up, lies in a time relay with still connect in parallel between the alternating current power supply and be provided with constant voltage power supply, constant voltage power supply will alternating current power supply exports after converting the steady voltage direct current into, stabilized power supply output end with the dew point hygrometer is connected, dew point hygrometer and vacuum meter are connected with the body valve of transformer, reactor through measuring the cable. The utility model discloses can not only the real -time supervision transformer, the vacuum of reactor, can monitor the dew point of gas bleeding moreover to the condition of getting rid of of indirect judgement ware body surface moisture can be used in the ware body drying of transformer, reactor and vacuum oil injection technology.