A liquid level detecting method is provided. Firstly, a receiving component is provided, wherein the receiving component includes a transmissive container for containing a liquid and a marking component located on a rear surface of the transmissive container. Then, a camera captures a receiving component image of the receiving component from a front surface of the transmitting container, wherein the receiving component image includes a transmissive container image and a marking component image. Then, the marker component image is analyzed downward from an end portion to obtain multiple width values of multiple position points of the marker component image. Then, a width difference between each width value and a width average of the marking component image is obtained. Then, a position point whose width difference value is not within a preset range is determined. Then, according to the position point, a liquid level of the liquid is determined.