The invention discloses an alignment coupling piece for the optical module of a liquid crystal display, which comprises a substrate of which the two sides are an incident surface and an exit surface, and is characterized in that: the incident surface consists of at least two ridge prism arrays which are arranged in parallel and transparent surfaces which space the ridge prism arrays; the exit surface consists of reversed cone prism arrays of which the number is the same as that of the ridge prism arrays and reflecting surfaces; the ridge prism arrays consist of a plurality of strip ridge prisms which protrude from the transparent surfaces and are arranged in parallel; the reversed cone prism arrays consist of a plurality of strip reversed cone prisms which are arranged in parallel; the cone tip parts of the reversed cone prisms are light reflecting parts; the non-light reflecting parts of the reversed cone prisms are light exit parts; and the reversed cone prism arrays are spaced by the reflecting surfaces. The alignment coupling piece has the advantages of avoiding alignment requirements on an incident backlight beam, ensuring the effective utilization of a backlight source, improving the brightness and contrast of the liquid crystal display, greatly reducing the thickness of a beam pressing slice and reducing the thickness of the liquid crystal display.