ITO (indium tin oxide) film of a high transmittance and high conductivity has been extensively studied because of its applications in optoelectronics. In this study, ITO nano-powder was prepared by constant pH chemical coprecipitation method. The experimental results show the precursor of the powders play a key role. The optimum was selected with orthogonal experiments. The optimum showed pH 8.5, temperature 60 °C, solution of indium and tin adding speed 100 mL/min, stirring rate 500rpm, additives 25 mg/L. the primary particle size is less than 10 nm with narrow distribution and good decentralization. SEM shows that particles are sphere-like and XRD shows that precursor consist of indium hydroxide and amorphous body. Zeta potential showed the powder is in nanoscale with uniformly dispersiveness. ITO nanocrystalline powder was formed after sintering at 600°C.