Antimony-doped tin oxide (SnO2:Sb, ATO) films have been deposited on glass substrates using atmospheric pressure chemical vapor deposition (APCVD) method. The precursors are mixed with SnCl4, SbCl5, and O2 to prepare the films. This study used synchrotron grazing incidence X-ray diffraction (GIXRD) to investigate the film microstructure. Our results show that the precursors of chlorine ions were involved in the doping mechanism, causing the microstructure of films to change slightly. The film has an average transmittance between 85.8 and 82.1% within a visible spectral range from 400 to 800 nm. The minimal resistivity was 6:1 × 10 -4 ωcm after doping. The synchrotron GIXRD data show that the chlorine ions caused the lattice constant change. A possible mechanism was proposed to explain the enhancement in electrical property due to chlorine dopants.