The objects with mesostructure surfaces have complex model structures, which result in low efficiency of ambient occlusion algorithms. To improve the rendering speed, a screen-based ambient occlusion method was proposed. By using off-screen technique, only the points which can be seen were to determine the occlusion. The algorithm has two render passes: First, the depth texture of the whole scene was obtained; At second pass, the effect of ambient occlusion could be quickly computed by finding the maximum of the block angle. The ambient occlusion of the whole scene could be rendered by the deferred shading technology. The algorithm runs entirely in image space, and uses graphics pipeline to show the ambient occlusion effect of deformable objects in dynamic scenes. Experimental results show that the proposed method is more efficient than the available methods, as this method doesn-t need any pre-processing, and the time used for ambient occlusion determination is less.