Pressure fluctuations in a three phase bubble column reactor operating at relatively low pressure(92KPa) have been analyzed by adopting the spectral and fractal analyses to get the engineering informations for the on-line con-trol and fault diagnosis of the reactors. The mean value, standard deviation. skewness and kurtosis of the pressure fluc-tuations have been obtained. The local fractal dimension has been determined from the Pox diagram obtained by means of the rescaled range analysis of the pressure fluctuations based on the fractional Brownian motion. The local fractal di-mension of pressure fluctuations has increased and thus the pressure fluctuation signals have become less persistent and ir-regular, with increases in the gas flow rate, reaction temperature, particle size and solid content in the slurry phase. The local fractal dimension has been well correlated in terms of the operating variables.