A beam diffusing module including a light incident terminal, a light emitting terminal, a first reflective plate and a second reflective plate is provided. The first reflective plate and the second reflective plate are disposed on a transmission path of a laser beam. At least one of the first reflective plate and the second reflective plate has a plurality of reflective micorstructures. The reflective micorstructures are arranged along a second direction from the light incident terminal towards the light emitting terminal. At least a part of the laser beam enters the beam diffusing module through the light incident terminal and emerges from the light emitting terminals after being reflected repeatedly by the first reflective plate and the second reflective plate to cause an M squared of the laser beam to be redistributed along a first direction. A beam generating system is also provided.