The present invention relates to an optical medium judging method for avoiding the collision of an objective lens with a disk or the failure to judge a warped disk when the optical disk drive judging the disk. This method will move the objective lens so as to obtain the data of the laser beam reflection amount of the focusing beam on the plastic layer of the optical disk. By using the reflection amount, the driving circuit will output a rising direct current voltage of a voltage difference to drive an actuator so as to move the objective lens to a proper position capable of judging the disk without colliding with the disk.