PURPOSE: An apparatus and a method for automatically positioning the roll gap of a thick plate rolling mill are provided to shorten time and improve setting accuracy by automatically setting a pass line position and deciding the initial position of the roll gap not by the manual operation which is complicated, and has errors generated and danger of facility damage due to mistakes. CONSTITUTION: The method for automatically positioning the roll gap of a thick plate rolling mill comprises the steps of first step (410) of deciding a pass line position by calculating a pass line height and ascending a hydraulic cylinder to a calculated height; second step (420) of descending a screw motor until a rolling load reaches to the first target value that is set lower than a standard rolling load during the initial setting of a roll gap; third step (430) of ascending the hydraulic cylinder so that the rolling load becomes the standard rolling load during the initial setting of a roll gap, a second target value when the rolling load reaches to the first target value; and fourth step (440) of ascending a screw to a position for preparing rolling so that the initial positioning of the roll gap is completed after remembering positions of the screw and the hydraulic cylinder at that time and descending the hydraulic cylinder as low as a certain value when the detected rolling load reaches to a second target value.