The invention belongs to the field of pose regulation of collimators and discloses a collimator pose regulating device and a collimator pose regulation method for free-form surface laser assisted milling. The device comprises an inside engaged gear, a circular sliding rail and a cross sliding table mechanism; the inside engaged gear comprises a main gear and a pinion, wherein the main gear is installed outside a main shaft of a machine tool in a sleeving manner; the pinion is internally engaged with the main gear; the lower portion of the main shaft of the machine tool is connected with a cutter; the main gear is fixed to the main shaft of the machine tool; the pinion is connected with a first servo motor; the circular sliding rail is installed outside the main shaft of the machine tool ina sleeving manner; the cross sliding table mechanism is positioned by the side of the main gear, is connected with the first servo motor and can do circular motion with motion of the pinion under theguidance of the circular sliding rail; a collimator is installed on the cross sliding table mechanism by virtue of a mounting and fixing mechanism; and the method is implemented by utilizing the collimator pose regulating device. The collimator pose regulating device disclosed by the invention can be used for regulating a laser spot in real time according to any cutter moving route so that the laser spot can be always positioned at a specified position of a material in front of the cutter.