The characteristics and mechanism of pressure fluctuations in a CFB riser were investigated with the measurement on dynamic pressure of a gas-solid two-phase flow in a φ200 mm×12500 mm riser using FCC catalyst.The mass flux of solids in the riser was varied in the range 0 to 250 kg8226;m-28226;s-1 and the superficial gas velocity was 5.6 m8226;s-1.Pressure transducers were employed to evaluate the axial pressure profile，especially the dynamics pressure along the riser.The experimental results show two types of pressure fluctuations in the riser.One is at low frequency and high amplitude，which is resulted from unstable feeding to the riser

and the other is at high frequency and low amplitude，which is the resultant of a variety of factors，such as cluster movement，gas-solid interaction and gas velocity fluctuation.The dynamic behavior of the pressure fluctuation is characterized by Fourier spectral analysis.The standard deviation and power spectral density of pressure fluctuations indicate that the intensity of pressure fluctuations increases with solid mass flux，but it attenuates in some degree along the axial direction of the riser.The dimensionless power spectral density shows that the fluctuations at low frequency and high amplitude are similar along the axial direction of the riser.