Abstract: A method for focal spot reconstruction and far-field focal spot measurement based on the orthogonal wedges is proposed. In order to verify the validity of the method in extracting focal spot side lobe data, expanding measurement dynamic range of CCD and improving measurement precision of laser beam quality, the beam quality factor is taken as a useful evaluating measure here, the theoretical model of intensity profiles of the defocus spot is build and the laboratory scheme accordingly is implemented. The results show that, compared with the traditional measurement method, this method makes the dynamic range of CCD expand about 9 times, plenty of intensity information of the focal spot side lobe emerges from random noise of CCD, and the measurement precision of the beam quality factor is improved about 16%.