To investigate the feasibility of industrial preparation of nano-silica process by pretreated rice husk combustion in fluidized bed, the combustion test of pretreated rice husk was carried out in a bench-scale fluidized bed and active rice husk ash (RHA) samples were obtained. Scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, X-ray fluorescence spectrometer and specific surface area and pore size analyzer were used to characterize the microstructure and physicochemical properties of bed material and RHA, and then the effects of acid pretreatment on the combustion state of rice husk in fluidized bed and the performance of RHA were deeply studied. The results showed that the pretreated rice husk burned well in the bench-scale fluidized bed and the bed material′s agglomeration was not happened. The obtained RHA consisted of 15-50 nm nanoparticles and had abundant mesoporous pores of about 4 nm, SiO₂ purity of higher than 98 wt.% and ultra-low residual carbon content of less than 0.08wt.%. Acid pretreatment greatly eliminated the limitation of combustion temperature on RHA properties under low temperature condition, however, the temperature constraints gradually appeared when temperature above 800 ℃. In brief, the fluidized bed combustion of acid-pretreated rice husk could achieve the purpose of preparing high purity and high active RHA, and the pretreatment effect of sulfuric acid was better than citric acid.