Solid circulation behavior in a cylindrical spouted bed of 0.205 m diameter with a draft tube is studied based on the power spectral analyses of the time series data of pressure fluctuation and optical signals measured by optical fiber probes in the draft tube and the entrainment region. The effects of solid particle size, bed mass and the length of the entrainment region on solid circulation are examined, in the low gas velocity region, solid particles move from the annulus into the gas jet to form clusters and are carried upward in the draft tube with a frequency of 7-10 Hz. In the high gas velocity region, solids flow is in a stable pneumatic convey state, As the particle size increases and the bed mass decreases, the frequency of clusters is reduced by the promotion of gas by passing, leading to a decrease in solid circulation rates. In the pneumatic transport regime, the larger particle system exhibits a higher solid circulation rate. The extent of the length of the entrainment region decreases the frequency of clusters but increases the solid circulation rate by virtue of increasing the! size of clusters.