Characteristics of gas-liquid-solid flow behavior in a riser are investigated in a three-phase circulating fluidized bed (0.102 m I.D, x 3.5 m in height). Local gas holdup, solid holdup distribution, and pressure fluctuations in the riser have been measured and utilized to describe the gas-liquid-solid now behavior more conveniently. The resultant pressure fluctuations have been analyzed by adopting the chaos method: The time series of pressure fluctuations have been interpreted by means of phase space portraits and Kulmogorov entropy. The effects of gas and liquid velocities and solid circulation rate on the local gas holdup, solid axial distribution, phase space portrait, and Kolmogorov entropy of pressure fluctuations, as well as on the flow behavior of gas-liquid-solid mixture in the riser are determined, It is found that pressure fluctuations can be a quantitative tool to characterize the flow behavior and flow regime transition of multiphases in the riser The relations between the pressure fluctuations and the distribution of phase holdup and now regime in the riser are also discussed.