The utility model relates to an SAW (surface acoustic wave) sensor adopting a three-dimensional nano-structure. The SAW sensor comprises a piezoelectric substrate, an input interdigital electrode IDT1, an output interdigital electrode IDT2 and a sensitive area, wherein the input interdigital electrode IDT1 and the output interdigital electrode IDT2 are parallelly arranged on the surface of the piezoelectric substrate; the sensitive area is located between the input interdigital electrode IDT1 and the output interdigital electrode IDT2; a three-dimensional nano-structured sensitive membrane is arranged on the sensitive area and comprises modified three-dimensional nano-wires or nano-tubes growing on the sensitive area as well as a sensitive membrane applied to the surface of the sensitive area; and the modified three-dimensional nano-wires or nano-tubes are three-dimensional nano-wires or nano-tubes coated with the sensitive membrane on the outer surfaces. The SAW sensor adopting the three-dimensional nano-structure has high integration level, small size, light weight, low cost and wide application range, can work at room temperature, has high sensitivity during detection of a low concentration gas, and more importantly can detect various gases quickly and reliably.