An image brightness adjustment method and an image brightness adjustment device are provided in the present disclosure. A brightness of a fluoroscopic image obtained by irradiating an object with an initial fluoroscopic dose of X-rays is acquired as an initial brightness. A current load corresponding to the initial brightness is determined according to a relationship between image brightness and loads for the initial fluoroscopic dose, where the current load indicates an X-ray blocking ability of the object. Then, a stable fluoroscopic dose corresponding to the current load is determined according to a relationship between load and stable fluoroscopic dose, where the stable fluoroscopic dose is used to obtain a fluoroscopic image of a predetermined brightness for the object.