An autofocusing system used for a laser burst-cutting-area (BCA) marking system for a DlVX production line has been developed. The principle of focus error detection is based on a method that takes advantage of the focusing properties of simple optical elements. A differential detection method is used to achieve high resolution, and a position servo is designed to accomplish the autofocusing. Some design considerations, system modeling, simulation, and experiments are described. Experimental results are presented to show the feasibility of this system.