During laser micro-machining, the constant control of laser energy density is a key technology to improve the processing precision. This paper presents a laser spot size of real-time detection and control system design on the base CCD and FPGA processing technology. Using CCD video signal binarization method and FPGA processing technology, we realized real time detection and control of spot area on the workpiece to achieve a constant purpose. The relative measurement error of spot size is very small as maximum 0.5 percent, the resolution of spot size measurement is less than 10μm2. This system can be directly applied to control of laser spot in laser micro-polishing.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.