The present invention provides a large-capacity preparation flow cell with an optical fiber interface, which comprises a flow cell body, a flange connector, a plurality of adjusting rods, a quartz light column, a light column sealing gasket, a light column sealing pressure plate, a light column adjusting piece, a flat convex lens holder, a flat convex lens, a flat convex lens gasket, an optical fiber adapter, a standard optical fiber connector, an adjusting rod sealing gasket, an adjusting rod sealing pressure plate and a plurality of cell nuts. A detection area is formed between the opposite adjusting rods on the left side and the right side, and the end face of the standard optical fiber connector is arranged at the focal point of the flat convex lens, so that parallel light can be transmitted into the detection area. The present invention has the advantages that the optical path of the large-capacity preparation flow cell can be adjusted conveniently according to the difference of the concentration and light absorbance of materials to be tested, so that the detected values fall into the detection range of a detector. In addition, the flow cell can be arranged away from the detector due to the optical fiber interface, so as to facilitate explosion-proof applications.