Abstract: A fast algorithm for calculating local statistics in frequency domain is presented. The convolution operator is constituted by means of the nature of local statistics. It is circularly convoluted with images to complete fast operations. The circular convolution operator is compared with the linear convolution operator in the calculation of local statistics. The distinguishel feature of the present algorithm lies in that its computing time and storage requirement is independent of the size of the local window. The experiment on plant chromosome images shows that the present algorithm is about 6 times as fast as the direct space domain calculation.