A spectrometer (100) and an optical input portion (32) thereof are disclosed. The optical input portion (32) comprises an assembly structure (322), and the assembly structure (322) is formed at a hole wall (321) of a through hole (3211) of the optical input portion (32). A light (L1) is incident into a dispersing element (2) of the spectrometer (100) along an optical path (13) after passing through the through hole (3211), and is dispersed by the dispersing element (2). The assembly structure (322) is used to be detachably assembled with an optical element (200). When the optical element (200) is assembled with the assembly structure (322), an optical axis of the optical element (200) is linked to the optical path (13). As a result, the light (L1) passing through the optical element (200) is incident to the dispersing element (2) along the optical axis and the optical path (13).