The invention is an optical fingerprint sensor with prism module, including a shell; an optical prism arranged in the shell, the optical prism comprising a collection surface, a basal plane, a mirror surface and an output surface, there being a first included angle provided between the mirror surface and the collection surface, a second included angle provided between the mirror surface and the basal plane, a third included angle provided between the output surface and the collection surface, and a fourth included angle provided between the output surface and the basal plane; and an image sensing unit combined with the shell, comprising multiple luminous elements arranged beneath the basal plane of the optical prism correspondingly, and an image receiver and a lens arranged corresponding to the output surface. Thereby, an user is allowed to place fingerprint onto the collection surface for a light source of the luminous elements to be input from the basal plane and irradiated onto the fingerprint, and a light ray undergoes a first reflection and a second reflection with the basal plane and the mirror surface, respectively. After that, the output surface acts as a background surface and a light ray output as the light ray undergoes the second reflection for the image receiver to receive the light ray and form a fingerprint image, such that the advantages of maintaining an optical path effectively and reducing the volume of the optical fingerprint sensor are accomplished.