An apparatus for measuring the liquid level of molten metal including an image measuring device (5), a measuring probe (6), a lifting mechanism (1), a displacement sensor (11), an data processing system (4) and a correction marker(7). The lifting mechanism (1) is fixed to the molten metal container (10) or is independent of the molten metal container, the image measuring device (5) and the measuring probe (6) are installed on the lifting mechanism (1) or are independent of the lifting mechanism, and the optical axis of the image measuring device (5) is set at an angle with the geometric axis of the measuring probe (6), the measuring probe (6) is located within the field of view of the image measuring device (5), the image measuring device (5), the lifting mechanism (1) and the displacement sensor (11) are connected to the data processing system (4) respectively. A method for measuring the level of molten metal is also disclosed. The present invention is able to eliminate the influence by the slag layer floating on the molten metal and to achieve stably and continuously accurate measurement of molten metal level by using the measuring probe (6) inserting into molten metal through the slag-metal interface and having the slag thickness information after lifted.