In solar adaptive optical system,absolute difference algorithm and correlation coefficients algorithm are widely used in Shack-Hartmann wave-front detection of the extended object.A Shack-Hartmann wave-front processor based on absolute difference algorithm is described in this paper.Real time wave-front processing of a system with 6×6 sub-aperture array,which is 32 pixels×32 pixels in size each and for which the reference image is 16 pixels ×16 pixels,is accomplished in a single Field Programmable Gate Array(FPGA) chip with absolute difference algorithm.The peak operation speed is over 23 000 000 000/s and calculation latency is 120 μs.Using this processor,frame rate of the Charge Coupled Device(CCD) can be up to 1 000 Hz.The design is realized in a single FPGA and it is low-cost,compact and easy to be modified.