A muzzle flash simulator for use in an airsoft gun, comprising an internal passage, a detector, a controller, and multiple illuminating components. In response to a projectile passing through and away from the internal passage, the simulator will be triggered and flash multi-color lights on a projectile passage in front of the simulator. When each color light is illuminated on the moving projectile at a specific intensity at specified time periods, because of an afterimage phenomenon of the human eye, the surface of the moving projectile reflects the corresponding color and leaves a multi-layered light-trail accordingly.