To meet the request of real-time control and the flexility of the Stochastic Parallel Gradient Descent (SPGD) algorithm for Adaptive Optics (AO) system, an implementation of the SPGD algorithm in FPGA was proposed. Firstly, the diagram of the SPGD algorithm controlling system was designed. Then, the key modules were processed for real-time control, and a deformable-mirror controlling module that can be updated for future application was designed according to the pipeline and RAM techniques. Based on this implementation, a laser beam focusing system with a 61-element deformable mirror and high frame-frequency CCD was built. The experimental results demonstrate that the AO system can correct static distorted wave-front successfully with different system performance metrics and can also control deformable mirror and tilt mirror simultaneously.