The invention provides a method for preparing a monodisperse indium oxide nanometer porous microsphere, and belongs to the technical field of function materials. The preparation method particularly comprises the following steps: adding citric acid with a certain molar ratio in indium chloride aqueous solution, mixing intensively, adding moderate urea as a precipitant, and dispersing uniformly; sealing the mixed solution in an autoclave and conducting water thermal reaction for a period of time, and then centrifugalizating, washing and drying; calcining in a muffle furnace in air to obtain the monodisperse indium oxide nanometer porous microsphere. The method provided by the invention has low cost, simple manufacturing technology, high productivity, and is easy to realize industrialization and mass production. The indium oxide nanometer microsphere produced by the method has a neat appearance, uniform disperse, has a porous structure and a larger specific surface area, and can be applied in the field of solar cells, FPDs (Flat Panel Display), photo-electron devices, gas sensors and the like.