The blur direction and blur length are two key parameters to recover motion-blurred images.In view of the defects that low precision and the limitation of angle range in the method of detecting center bright stripe of Fourier spectra image.Based on the analysis of the mathematical principle of Radon transformation and the causes of cross-shaped bright line and its interference, according to the characteristics of spectral images,the improved approach of using the dark line of Fourier spectra image to identify blur direction is proposed.After the binary image of Fourier spectra image is got, the skeletonisation of mathematical morphology is employed to make the width of dark line narrowed, then the Radon transform is employed to get the blur direction and blur length.The experiment results show that the proposed method can avoid the disturbance of cross-shaped bright line, and improve the precision and stability of the blur direction detection and enlarge the range of angle detection.The detection error of blur angle is less than 0.5˚, the range of blur angle detection is $0^\circ \sim 180^\circ$, it works better than traditional algorithms.