A composite prism for multi-functional telescopes, and binocular telescopic optical system thereof. The composite prism comprises a first half-pentaprism (2), a roof prism (3), and a second half-pentaprism (4). Longer right-angled surfaces of the first half-pentaprism (2) and second half-pentaprism (4) are cemented onto a bottom surface of the roof prism (3). A light incident plane of the roof prism (3) and a light emission plane thereof share the same one and are parallel to a roof edge of the roof prism (3), such that a light incident axis of the composite prism is parallel to a light emission axis thereof. A binocular telescopic optical path system comprises an objective lens (1), the composite prism, a reticle lens (5), and an eyepiece (6), and has functions of viewing, sighting, laser emitting and receiving, and display.