The invention relates to the field of biosensors, in particular to a carbon nanotube/polyaniline composite fiber-based transistor biosensor and application. The carbon nanotube/polyaniline composite fiber-based transistor biosensor comprises a source electrode and a drain electrode and a gate electrode which is intersected with the source electrode and the drain electrode; the source electrode andthe drain electrode are obtained by coating conductive silver paste on the surface of a carbon nanotube/polyaniline composite fiber, and the gate electrode is obtained by attaching oxidase to the surface of the carbon nanotube/polyaniline composite fiber through a fixing agent; the carbon nanotube/polyaniline composite fiber has a three-layer structure, wherein the innermost layer is fiber, the middle layer is a carbon nanotube, and the outermost layer is polyaniline with a linear structure. According to the invention, the polyaniline with the linear structure is more beneficial to improvingthe transfer of electrons and the transportation of ions, and the sensitivity of the transistor is significantly improved.