A laser interference lithography system with a pattern locking function comprises a laser, a reflector, a beam splitter, a substrate stage, a substrate and a pattern locking device. A laser beam emitted by the laser is split into an exposure beam and a reference beam by a spectroscope; the exposure beam passes through the beam splitter, and is reflected to the substrate on the substrate stage by the reflector to realize interference; the interference patterns can realize pattern record transfer by exposing the substrate; and the patterns are locked by the pattern locking device to prevent pattern drift during exposure. The pattern locking device includes a null phase meter, an electronic signal processing component, a controller, a driver and a phase modulation executing, wherein the null phase meter is used for measuring pattern phase drift; the pattern phase drift is fed back to the controller through the signal processing component; and the controller controls the phase modulation executer to realize phase locking through the driver. The laser interference lithography system provided by the invention has the advantages of simple structure, high pattern locking accuracy and the like, and is a key system for realizing large-area high-accuracy grating fabrication.