Abstract: It has been acknowledged that a dilute-phase/dense-cluster two-phase micro flow structure exists in the riser. The particle velocity signals from Laser Doppler Velocimeter are analyzed and the velocity and turbulent velocity of particles in the dilute phase are obtained. The radial velocity distribution of particles in the dilute phase is similar to a parabola. A correlation, similar to the 1/n power law of gas velocity in turbulent state, is given to describe the velocity distribution quantitatively. The cross-sectional average velocity of particles in the dilute phase is nearly equal to the superficial gas velocity, which indicates that the particles in the dilute phase exist in individual particle state. A maximum value exists at the radial position r/R=0.5—0.8 for the turbulent velocity of particles in the dilute phase. This radial position may correspond to the boundary between the dilute phase controlled region and the dense cluster controlled region.