The invention provides a large-aperture ultra-smooth surface defect detection device and method. The device mainly comprises a laser device, a laser beam expanding system, a high-reflectivity mirror, a polarizer, a polarization splitting prism, a 1/4 wave plate, a rotary prism, a telecentric field lens, a high-angle-scattering light detector, a low-angle-scattering light detector, a line triggering detector, a reflection light detector, a precise display platform and a computer. Detection efficiency of a large-aperture optical element can be remarkably improved, and the situation that detection results are severely influenced by vibration, axial jumping and the like, caused by high-speed rotation, of the large-aperture optical element is avoided. Surface defects can be classified, and it can be recognized whether the detected defects are pits, scratches, protruding dust, fibers and the like.