The invention provides a laser rapid fabrication method for flexible gallium nitride (GaN) photodetector which comprises the following steps: (1) bonding a flexible substrate to a GaN epitaxial wafer; (2) adjusting the focal plane position of a light beam, and ensuring that the light beam is incident from the side of a GaN epitaxial wafer substrate; (3) enabling the light beam to perform scanning irradiation from the edge of a sample structure obtained in the step (1); (4) adjusting the process parameters, and scanning irradiation in the reverse direction along the path in the step (3); (5) remove the original rigid transparent substrate of the epitaxial wafer to obtain a Ga metal nanoparticle/GaN film/flexible substrate structure; and (6) preparing interdigital electrodes on the surfaces of the Ga metal nanoparticles obtained in the step (5). The flexible GaN photodetector with Ga metal nanoparticle in-situ distribution detection surface is prepared in one step through laser technology, the process is simplified, meanwhile, the surface of the detector is induced to form the surface plasmon resonance effect, the light absorption and light response performance is greatly enhanced, and the flexible gallium nitride photodetector is suitable for industrial production.