The invention belongs to the field of collimator position and posture adjustment, and particularly discloses a collimator position and posture adjustment device and method for laser assisted milling.The collimator position and posture adjustment device comprises a fixed supporting plate, a pair of parallel square slide rails, a U-shaped movable supporting back and a cross slide platform mechanism, wherein the pair of parallel square slide rails is installed on both sides of the fixed supporting plate, and two fixed supporting backs are correspondingly mounted at the ends, away from the fixedsupporting plate, of the two square slide rails; and the two fixed supporting backs are connected with the U-shaped movable supporting back in pivoted and rotating modes so as to form a rotary pair, the cross slide platform mechanism is mounted on the U-shaped movable supporting back, and a collimator is mounted on the cross slide platform mechanism. The method is performed by using the collimatorposition and posture adjustment device to achieve the adjustment of the laser incident angle, spot size, and the relative position between a laser spot and a tool. The collimator position and postureadjustment device can effectively adjust the position and posture of the collimator, has a compact overall structural layout, small size and small space occupation.