Abstract Wide bandgap semiconductors, particularly In 2 O 3 :Sn (ITO), are widely used as transparent conductive electrodes in optoelectronic devices. Nevertheless, due to the strohave beenng scattering probability of high‐concentration oxygen vacancy (V O ) defects, the mobility of ITO is always lower than 40 cm 2 V −1 s −1 . Recently, hydrogen‐doped In 2 O 3 (In 2 O 3 :H) films have been proven to have high mobility (>100 cm 2 V −1 s −1 ), but the origin of this high mobility is still unclear. Herein, a high‐resolution electron microscope and theoretical calculations are employed to investigate the atomic‐scale mechanisms behind the high carrier mobility in In 2 O 3 :H films. It is found that V O can cause strong lattice distortion and large carrier scattering probability, resulting in low carrier mobility. Furthermore, hydrogen doping can simultaneously reduce the concentration of V O , which accounts for high carrier mobility. The thermal stability and acid–base corrosion mechanism of the In 2 O 3 :H film are investigated and found that hydrogen overflows from the film at high temperatures (>250 °C), while acidic or alkaline environments can cause damage to the In 2 O 3 grains themselves. Overall, this work provides insights into the essential reasons for high carrier mobility in In 2 O 3 :H and presents a new research approach to the doping and stability mechanisms of transparent conductive oxides.