The invention discloses a central fishtail cutter and belongs to the field of parts of shield tunneling machines. The central fishtail cutter comprises a cutter holder, a first cutter body, an additive injection block and two second cutter bodies, wherein the two second cutter bodies are respectively and symmetrically arranged on two sides of the first cutter body and are vertically fixed on the first cutter body; the bottoms of the two second cutter bodies are fixed on the cutter holder; a second accommodation groove is formed in a position, corresponding to the additive injection block, of each second cutter body; the additive injection block is located in an accommodation cavity and is mounted in an additive injection block mounting hole; injection channels are formed in the first cutter body and the two second cutter bodies; a plurality of injection holes are formed in the position, corresponding to the accommodation cavity, of the additive injection block; the lower injection holes are connected with the injection channels through connection tubes. Through the central fishtail cutter, the injection channels of the first cutter body and the second cutter bodies are capable of guiding additives in the additive injection block to outlets of the injection channels through the connection tubes, so that the injection range of the additives can be broadened; the problem of formation of mud cakes can be effectively avoided.