An LED comprises a substrate, a first semiconductor layer, an active layer, a second semiconductor layer, a first electrode and a second electrode. The first semiconductor layer, the active layer, and the second semiconductor layer are stacked in that order and located on a surface of the substrate. A number of first three-dimensional nano-structures are located on a surface of the second semiconductor layer away from the active layer. The first three-dimensional nano-structures are linear protruding structures, a cross-section of each linear protruding structure is an arc. The present disclosure also relates to an optical element.