The invention discloses a nanometer TiO2-based low-power consumption micro-nano gas sensor and a preparation method thereof. The sensor is provided with an SiO2-Si3N4 masking layer, a silicon substrate, an SiO2-Si3N4-SiO2-Si3N4 composite insulation layer, an electrode layer and a sensitive material layer from bottom to top; by arranging a temperature measurement electrode, the temperature in the center of a chip is measured in real time; a majority of Si under the Si substrate is corroded and removed through a wet method to form an SiO2-Si3N4-SiO2-Si3N4 composite floating film structure, a heating electrode and a sensitive electrode which are spirally arranged in a central symmetry manner are arranged on the floating film; and a sensitive material is arranged on the sensitive electrode, and a TiO2 film and a Ti film are sequentially sputtered in a sensitive material region, wherein the TiO2 film is used for defining a growth region of a subsequent nanorod, and a Ti source is oxidized to form a TiO2 nanorod to prepare a sensitive layer through a hot hydrochloric acid steam method to enable the TiO2 nanorod to grow on the TiO2 film. The nanorods are bridged and connected to each other, so that the nanometer TiO2-based low-power consumption micro-nano gas sensor has a very high specific surface area and a better gas response characteristic; the mechanical performance of the floating film is optimized, heat transfer is reduced, and the temperature is accurate and controllable; and the procedure is simplified, and the generation of a parasitic electric field is prevented.