The invention discloses an early-warning device for the warning level of an oil cup of an extractor hood. The early-warning device comprises a magnetic part (1), a float (2) floating on the oil surface of the oil cup of the extractor hood, a guiding device installed in the oil cup of the extractor hood and a magnetic proximity switch (4) arranged above the magnetic part (1) and connected with a controller of the extractor hood, wherein the float (2) is installed on the guiding device, and the magnetic part (1) is arranged on the float (2). With the early-warning device, a user does not have to notice the oil level in the oil cup of an extractor hood all the time. Once the oil level in the oil cup reaches a certain height, the early-warning device reminds the user to pour out the oil. The early-warning device is very convenient.