Considering the development trends and demands of large-aperture prime focus optical telescopes， design and alignment methods for a large-aperture prime focus optical system were analyzed. A prime focus optical system with a large aperture was presented. This system was composed of an aspherical primary mirror and six spherical lenses with smaller apertures. The corrective lens could be used to enlarge the field of view， correct image aberrations， and ensure the image quality of the system. This system has a focal length of 1 300 mm， working waveband of 0.4-0.8 μm， clear aperture of 1 000 mm， and a 2.7°×2.7° field of view. In addition， this system was compensated by moving the detection image plane in the range of -40-+50 ℃. The modulation transfer function （MTF） of the system was above 0.45 at the Nyquist frequency， and the RMS speckle radius was less than 10 μm in the full field of view. A general method including the adjustment of the primary mirror， corrective lens， and system was proposed for this system， the results of which indicated that the star point 80% energy concentration degree in the full field of view of the system was in a 3×3 pixels region of the target area.