The invention discloses an optical refractive index change-based ultra-wideband neutron detector and belongs to the technical field of nuclear radiation detection. The optical refractive index change-based ultra-wideband neutron detector comprises a detection unit composed of a hydrocarbon material layer, a cesium iodide layer, a semiconductor and a substrate which are sequentially fixed, a high-voltage power supply and a neutron beam. A first metal film and a second metal film are respectively electroplated on the outer surface of the hydrocarbon material layer and the outer surface of the substrate. The first metal film is electrically connected with the negative electrode of the high-voltage power supply. After the neutron beam is incident on the detection unit, neutrons collide with protons in the hydrocarbon material layer to generate back-flushing protons. The back-flushing protons enter the cesium iodide layer to generate free electrons. Under the electric field action of a negative high voltage between the first metal film and the second metal film, generated free electrons in the cesium iodide layer are injected into the semiconductor, so that the optical refractive indexof the semiconductor is changed. The detector can convert the neutron beam into the refractive index change of the semiconductor material. Based on the optical interference, the refractive index change of the semiconductor material is measured, and then the intensity information of the neutron beam is obtained.