The invention discloses a concave grating-based cuboid portable Raman spectrometer. The concave grating-based cuboid portable Raman spectrometer comprises a casing bracket, a lens fixedly mounted on the side wall of the casing bracket, a 45-degree edge filter, a condensing lens and a gap, a reflector and a detector, wherein the 45-degree edge filter, the condensing lens and the gap are mounted on the central line of the lens in sequence; the reflector is arranged on a straight line where the central line of the lens is located, is fixedly mounted on the rear side of the gap and is used for changing the transmitting direction of a Raman signal penetrating through the gap and reaching a concave grating; a detector is fixedly mounted on the side edge of the reflector, the long edge of the detector is perpendicular to the straight line, and a perpendicular point, which is perpendicular to the straight line, on the long edge of the detector is located on the back surface of the reflector; the concave grating is fixedly mounted in the face of the detector and is used for receiving the Raman signal reflected by the reflector. According to the concave grating-based cuboid portable Raman spectrometer, by addition of the reflector, a light path is deflected; incident light of the spectrometer with the straight line and the long edge of the detector are in a perpendicular relation, and the light path is folded, so that a limited spectrometer space is effectively used, and the spectrometer is of a regular and compact quadrilateral structure.