We investigate the crystal structure and the spontaneos evolution of the silver oxide(Ag2O) ultrafine particles(UFP) produced by the vacuun-sputtering method.By using transmission electron microscopy and wide angle X-ray diffractometer and X-ray photoelectron spectrometer,the morphology and nanostructure and size distribution of UFP were measured and analysed.The process of the spontaneos evolution of UFPs was discussed by the spectrum fractal and thermodynamic potential and size-dependence of particles.It was suspected that the self-reduction decrystallization and decompose of crystal Ag2O UFPs might be intrinsic property of the ultrafine structure when the size of aggregate was less than the critical value.Furthermore,The reduced silver atoms have secondary recrystallization effect.