Abstract: A subsidence sensing device with a liquid replenishing mechanism has multiple liquid storage tanks connected with each other via communicating tubes, multiple level sensors, a liquid feeding tank disposed higher than liquid surfaces of liquids in the liquid storage tanks, and an air inlet tube and a liquid feeding tube communicate the liquid in the liquid storage tanks and feeding liquid in the liquid feeding tank. When the liquids in the liquid storage tanks evaporate gradually due to surrounding temperature or humidity, the feeding liquid in the liquid feeding tank flows into the liquid storage tank and replenish all of the liquid storage tanks via the communicating tubes. Thus, the liquid surfaces of the liquids in the liquid storage tanks can be kept at a predetermined proper liquid level, so as to allow the level sensor to provide accurate signals to monitoring staffs.