Fourier transform image-processing technology was applied to measuring the fiber size of hardwood. In this method，each cell was mapped by the center point on the cell in the transverse section with extending up and down by four pixels (nine-pixel length in total) and by two pixels in width, and thereafter line convoluted dot map (LCDM) was obtained. Through Fourier transform, the frequency distribution of power spectrum pattern from both horizontal and vertical directions was obtained and the cell diameter in radial and tangential direction was known from the maximum value except 0 in the distribution. The result indicates that there is no significant difference from that by optical microscope or image-processing software. It suggests that the method can be applied to the cell measurement and expand the Fourier transform application domain. This method provides the new research direction for the microscopic analysis and cell identification, and also provides a theoretical basis for the establishment of the mathematical model to identify cell geometric parameter.