In order to detect the formaldehyde content in building interiors, ZnO nanowire was used as the target for monitoring formaldehyde. ZnO nanowires were synthesized by hydrothermal method using zinc chloride (ZnCl2) and sodium citrate (C6H5Na3O7) as raw materials. The crystal structure and micromorphology of the prepared ZnO nanowires were analyzed by XRD, SEM and EDS. Structural characterization results show that the prepared ZnO nanowires have good crystallinity and high purity, with an average diameter of (39±10) nm, a length of about 400 nm, and good dispersion. As-prepared ZnO nanowires were brushed-coated on a ceramic tube, assembling into a gas sensor, and investigated systematic gas-sensing properties of sensor. The gas sensing test results show that the ZnO nanowire-based gas sensor has excellent gas-sensitivity properties to HCHO gas, and obtain a maximum sensitivity of 15.2 to 50×10-6 HCHO gas at the optimal working temperature of 125 ℃. In addition, it has good stability, reproducibility and selectivity.