Abstract: Aiming at the drawback of SSIM on blurry images,an improved Structural Similarity method for image quality assessment based on structure tensor is presented.Firstly,geometrical structure magnitude and orientation angle are extracted by local structure tensor.Secondly,a comparison function which is a structural orientation angle function and a structural magnitude function replaces the structure comparison function in the original SSIM.Finally,we use structure magnitude as a weighting function to derive the local quality map to obtain the final image quality evaluation value.The results show that since the importance of structure magnitude and orientation for the human eyes is more comprehensive consideration in perceiving structural information,the ST-SSIM is more accordant with the characteristics of human visual perception than SSIM.