A method for detecting optical film defects based on differential interference, comprising: an incident light is adjusted into a planar light wave, and the surface of an optical film to be detected is adjusted to be perpendicular to the planar light wave; the planar light wave sequentially passes through a diaphragm, the optical film, a first collimating lens and a lenticular lens, and then form two parallel outgoing beams by differential interference; the two parallel outgoing beams pass through a second collimating lens to form a differential interference image on a photodetector; and the differential interference image is analyzed to detect both superficial and internal defects of the optical film.