Abstract: In the active removal of space debris by the laser-driven method, it is assumed that the laser beams cover the whole debris assemble. This paper proposes to focus the laser beams into a small focal spot on the debris surface. A simple motion model is built to calculate the impulse and the attitude of the space debris of typical shape under a small laser spot irradiation. Fragments in shapes of sphere, cylinder and cube are selected. It is indicated that the momentum transfer by the laser ablation is related with the shape of the debris and the irradiated position. If the impulse direction is along the normal direction of the irradiated surface, the angular velocity of the debris will not change, on the other hand, if the impulse direction is not through the center of mass, the angular velocity and the attitude of the debris will change. The results of this paper may provide a theoretical basis for the active debris removal by the laser-driven method.