The electron transfer (ET) from the conduction band of the semiconductor to surface-bound species is a key step in the photocatalytic reaction and strongly affects the reactivity and selectivity, while the effect of catalyst surface structure on this process has rarely been explored due to the lack of an effective method. Herein, we have developed a strategy to detect and measure surface electrons' transfer energy to the adsorbates and disclosed a facet-dependent electron transfer energy over anatase TiO2. The photogenerated electrons are shallowly confined in the five-coordinated Ti atom (Ti5c) on the surface of the (101) facet with a transfer energy below 1.0 eV, while deeply confined in the six-coordinated Ti atom (Ti6c) on the subsurface of the (001) facet with a transfer energy higher than 1.9 eV. The different electron trap states strongly affect the ET process, thus regulating the photocatalytic activity. Taking formic acid (FA) dehydration as the probe reaction, a shallow trap of photoexcited electrons on the (101) facet of anatase TiO2 favors the dehydration of FA to CO, while a deep trap of photoexcited electrons on the (001) facet makes FA stable. Based on this knowledge, we successfully controlled the selectivity in the photocatalytic oxidation of biopolyols via selectively exposing the facet of TiO2. Through controlling the (001)/(101) facet, a wide range of biopolyols can be selectively converted into FA or CO with a selectivity of up to 80%. The present work disclosed a facet-dependent electron transfer process and provides a new horizon to the design of photocatalytic systems.