The present invention relates to a lens, a lens array and an illuminating device. The lens comprises a first surface and a second surface, wherein the first surface comprises: light incident surfaces, from which light enters the lens; and a total reflection surface, on which a part of light entering the lens is totally reflected, the second surface comprises a light emergent surface, wherein the light incident surfaces comprise a plurality of three-dimensional surfaces assigned to different light sources, a part of light from one light source enters the lens from one three-dimensional surface assigned to the one light source, and the other part enters the lens from one three-dimensional surface that is not assigned to the one light source. The lens has a compact structure and can uniformly mix colors.