Abstract: A novel multi-layer screen space ambient occlusion(SSAO) algorithm is presented to greatly reduce the linear computation cost scaling with the number of layers in the multi-layer SSAO algorithm.The sample point set used for ambient occlusion estimation at each pixel is divided into two parts.The first part is used to evaluate the depth complexity of the pixel and a maximum number of the required depth buffer samples are determined.The maximum number is then used to bound the number of depth samples taken from the buffer for the second part of the sample points.Experiments show that the algorithm achieves almost identical rendering results with the multi-layer SSAO algorithm and comparable efficiency with the single-layer SSAO algorithm.