The invention relates to a method for constructing morphological operators by using adaptive quasi-circular structural elements on the basis of a nonlinear structure tensor. For overcoming the shortcoming that by a linear structure tensor, inaccurate and even mistaken gradient information is easily estimated, the nonlinear structure tensor replaces the linear structure tensor at first, a feature value and a feature vector of the nonlinear structure tensor are calculated, then two measurement parameters including edge strength measurement and angular point strength measurement are defined, image features such as an edge region, a smooth region and corner are distinguished clearly, so that long semi-axes, short semi-axes and directions of adaptive oval structure elements are defined, in order to enable the obtained adaptive structure elements to be close to prefect oval shapes, the oval structural elements and original images are subjected to interpolation processing, and finally morphological operators such as adaptive corrosion, expansion, opening operation, closing operation and hit or miss transformation are redefined by the proposed adaptive quasi-circular structural elements. Confirmatory experiment results show that compared with other methods, the method has good effects in the aspects of structure adapting, angular point protection, filtering, target extracting and the like.