A method of evaluating an image quality for an imaging system and the imaging system are provided. The method may comprise: acquiring an image to be evaluated which is generated by the imaging system; extracting a plurality of sub-images from the image; obtaining a coefficient vector indicating a degree of sparsity by applying a sparse decomposition on the plurality of sub-images based on a pre-set redundant sparse representation dictionary; and performing a linear transformation on the coefficient vector so as to obtain an evaluation value for the image quality. The sparse dictionary is learned by only using a few high quality perspective images, and then the image quality is evaluated based on the sparse degree of the image which is obtained by using the sparse dictionary, thereby achieving a convenient and rapid no-reference image quality evaluation.