Liquid level adjusting device and method, lubricating system and lubricating oil replacing system

The invention discloses a liquid level adjusting device and a liquid level monitoring method, an engine lubricating system and a method for adjusting the liquid level of lubricating oil, a vehicle transmission lubricating system and a lubricating oil replacement system. The liquid level adjusting device comprises a first liquid storage tank, a second liquid storage tank and an air pressure adjusting device, wherein the second liquid storage tank is sealed, the first liquid storage tank and the second liquid storage tank are connected through a transmission component; and the air pressure adjusting device is connected with the second liquid storage tank and used for adjusting the air pressure in the second liquid storage tank, so that liquid stored in the first liquid storage tank and the second liquid storage tank flows interactively through the transmission component, and thus the heights of the liquid level in the first liquid storage tank and the liquid level in the second liquid storage tank can be adjust