Abstract: To accelerate the rendering by screen space ambient occlusion（SSAO）, we propose a novel method by exploiting the frame-to-frame coherence for local complexity. The basic idea is to design a local complexity for each pixel, and the pixels with similar local complexity have similar AO values. Thus, for a pixel in the current frame, its AO value can be obtained by reusing the AO value of the pixels in the previous frames that have similar local complexity, based on the frame coherence. In this way, much computation can be saved for acceleration. Moreover, we give a measure to avoid accumulation errors in reusing AO values. Experimental results show that our algorithm can improve the performance of SSAO by 10~40 percent without lowering the rendering quality.