Sn-doped indium oxide (ITO) film, due to the both distinctively transparent and conductive properties, is one of the most widely used transparent and conductive films, which has also been universally employed in various kinds of advanced opt-electron devices. In view of the advantages including facile preparation processes, superior performance and scalability, sputtering technique has been regarded as the optimal method for ITO film fabrication. The three critical parameters, namely oxygen flow rate, thickness and annealing process, were chosen to study the effects on the structure and optical-electrical properties of ITO films. In this work, ITO films were prepared by direct-current (DC) sputtering technology with argon (Ar) and oxygen (O2) mixed gases and ceramic ITO target. ITO films were also annealed under vacuum condition. The thickness was measured by contact profilometry (Taylor-Hobson Talystep). The film structure was detected by X-ray diffraction (XRD, Philips X′Pert). The element content was characterized by X-ray photoelectron spectroscopy (XPS). The UV/visible spectra were obtained using a spectrophotometer (Cary 5000, Varian, USA) with a wavelength from 800 nm to 300 nm. The sheet resistance of the ITO film was measured with a four-point co-linear probe method at room temperature. Afterwards, the comparable studies of ITO films obtained in the presence and absence of annealing process were also conducted, particularly the effects on the optical and electrical properties of ITO films. The electric resistivity of as-deposited ITO film slightly increases with the rise of oxygen flow rate, and increases dramatically with continuously increased oxygen flow rate. The resistivity of ITO film with 400 nm thickness reaches 8.0×10?4 ?.cm with the ratio of Ar∶O2 at 150∶8. The increase of thickness promotes to the low resistivity. Larger oxygen flow rate could directly promote the transparency of the ITO films. The annealing process under vacuum condition could increase the crystallinity of ITO film deposited at room temperature, giving rise to the low resistivity. Similarly, the annealed ITO film with large thickness obtains the low resistivity, and higher oxygen flow rate could also increase the resistivity. The ITO film shows the minimum resistivity of 2.7×10?4 ?.cm when the ratio of Ar∶O2 is 150∶6 and annealing temperature fixes at 500 ℃ under the vacuum condition. By tuning the ways of oxygen content and thickness to optimize the structure and oxygen vacancy content of ITO film, the sputtered ITO films with superior optical and electrical properties could be obtained at room temperature. The annealing process could improve the crystallinity of ITO film. The ITO film with the minimum resistivity of 2.7×10?4 ?.cm can be obtained through adjusting the three critical parameters, the crystalline ITO film with the lowest resistivity can meet the requirements from the scientific and engineering areas.