As the demand of ergonomics and bionics,more and more free-form surfaces appear in product design. In order to mark on these relatively large undulating surface with laser,the dynamic focusing and three-axis beam control technology must be adopted. The principle of beam focusing by dynamic expansion was analyzed,and the best range was determined from the relationship between the misfocus and the location,sizeofthe beam waist. A dynamic beam focusing mirror was designed,and a three-dimensional laser marking system was constituted together with X,Y directions galvanometer. Marking experiment of free-form surface verified the effectiveness of the system. This form of marking can be also used for the other two-dimensional surface.