The invention provides a thickening agent and application thereof. The thickening agent is prepared from the following materials in percentage by weight, 50-65% of surfactants, 15-25% of organic solvent and the balance of water. The thickening agent has the advantages that according to salt tolerance differences among the surfactants and intermolecular synergistic promotion effects, different types of the surfactants are selected for compounding and taking effect at different mineralization degrees; growth of rod-shaped and worm-shaped micelles is promoted along with salinity increase, the micelles are enlarged gradually, and accordingly, system viscosity is improved rapidly; the thickening agent has the characteristics of hypersalinity resistance, reutilization and the like, does not needchemical treatment under hypersalinity conditions, and can be directly applied to preparation of fracturing fluids or oil-displacing agents, and accordingly, reutilization of various types of flowback fluids is realized; an on-site construction mode of preparing the fracturing fluids by clear water-preparing the fracturing fluids by the flowback fluids-preparing the oil-displacing agents by the tail-end flowback fluids is adopted, and accordingly, zero pollution and zero emission in oil field operation are realized.