The effects of the U-o, PA/[PA+SA] ratio, total solid inventory and fluidizing velocity of loopseal on the axial solid holdup and the solid circulation rate have been determined with different particle sizes (174, 199, 281, 377 μm) and particle types (silica sand: narrow PSD, coal ash: wide PSD) in a CFB reactor with 3-loops. A simple model for solid hold-up based on the previous works was in agreement with the experimental data. With increasing U-o, G(s) increased exponentially, and in the center-loop, G(s) was 1.5 times larger than that found in the other side-loops. As the PA/[PA+SA] ratio increased, and as SA injection port was placed at a lower part in the riser, the axial solid holdup and G(s) increased. With increasing fluidizing velocity of loopseal to about 1.5u(mf), G(s) somewhat increased, but above the gas velocity of 1.5u(mf), the loopseal lost the ability of the control of G(s). The following correlation for the solid circulation rate in the CFB was developed with good accuracy; G(s)=φ (sys)[PA/TA](2.6)[H-f/H-T](0.5)[Ar](-1.88)[Fr](2.06)[KUo/U-t](-3.45).