The invention relates to preparation of a nano-fiber bundle transistor and application of the nano-fiber bundle transistor in ion sensing. The high-performance nano-fiber bundle transistor is prepared by polymerizing pyrrole monomers on a nano-fiber bundle in situ, and the nano-fiber bundle transistor is applied in an ion concentration sensor. Polypyrrole has good chemical and thermodynamic stability, biocompatibility and electric conduction performance, nano-fiber has stitchability, high specific surface area and high surface activity, and can be used for preparation and application of the high-performance transistor. The preparation method is simple in process, gentle in reaction condition, low in production cost, free of pollution and suitable for preparing the nano-fiber bundle transistor on a large scale, and has great application potential in electronic microcircuits.