In order to evaluate the far-field beam quality of 10 kJ-level laser facility with different off-axis wedged focus lens, by utilizing the methods of the sampling of weak light beams and amplification imaging of splitting beams, the focal spot data of 3ω laser was collected by two 16-bit scientific-grade CCD cameras in the paths of main lobe and side lobe under the conditions of that the lateral magnification coefficient is the same but the intensity attenuation coefficient is different. One CCD obtained main lobe of far-field image, the other acquired its side lobe. The far-field focal spot was reconstructed based on the mathematical model of schlieren method, and the dynamic range is 1 151.7∶1. The influence of CCD dynamic range, relative magnification ratio and system noise on reconstructed image was analyzed. Experimental results show that, the method can achieve a high dynamic range far-field accurate measurement of focal spot, the stitching error is less than one pixel, which meets the requirements of targeting experiments in experimental precision.