Controllable crystal facets exposing is an efficient approach for enhancing gas sensing performances of semiconductor nanomaterials. In order to study the crystal-facets-dependent gas-sensing properties of TiO2 systematically and exactly, a series of anatase TiO2 nanocrystals with different percentage of high-energy {001} crystal facets exposure (from 6% to 91%) were designed and synthesized by a simple hydrofluoric acid-assisted hydrothermal method. Gas sensing tests suggested that gas response of the TiO2 nanocrystals increased with the percentage of high-energy {001} crystal facets, although the specific surface areas gradually decreased. The results unquestionably confirmed the enhanced gas sensing activity of anatase TiO2 high-energy {001} crystal facets. Moreover, it was found that surface fluorination of high-energy {001} crystal facets played a negative role on the gas sensing activity. The relevant sensing mechanism was discussed in detail based on combination of experimental characterization and first-principle calculations, which showed that gas adsorption properties made a great contribution to gas sensing performance. By providing a comprehensive understanding of the crystal-facets-dependent gas-sensing properties of TiO2, the present work will be helpful for the designing of TiO2-based gas-sensing materials. (C) 2017 Elsevier B.V. All rights reserved.