The invention discloses a partial external prestressed and fine-grain reinforcing steel bar fiber reinforced cementitious composite (FRCC) railway box girder. The partial external prestressed and fine-grain reinforcing steel bar FRCC railway box girder comprises a hollow beam frame body consisting of a top plate and a webplate, wherein the top plate and the webplate are made from an FRCC material; an anchoring toothed plate and an anchoring diaphragm plate are symmetrically arranged on the two sides of the center in the hollow beam frame body; an anchor is arranged on the anchoring toothed plate; a diverter is arranged on the anchoring diaphragm plate; an external prestressed rib is arranged between the anchoring toothed plate and the anchoring diaphragm plate; and one end of the external prestressed rib is fixed on the anchor, and the other end of the external prestressed rib is fixed in the diverter. At the same time, an external prestressed technique has the advantages that: the partial external prestressed and fine-grain reinforcing steel bar FRCC railway box girder is convenient to construct, detect and change; and the friction loss of the prestressed rib is low, and the like. The webplate of the box girder is shrunk; the strength of the materials used by the box girder is improved; and the FRCC is used for substituting the conventional C50-grade concrete, the bearing capacity of the girder body is not reduced but increased, so that the box girder has an extremely wide application prospect.