Abstract: In designing fluidized-bed equipment, it is important to determine the TDH (Transport Disengaging Height) for the dilute-phase zone. Until the present time, the empirical curve developed by Zenz and Weil in 1958 has been widely used. In the present paper, on the basis of the equation for the motion of single particle, methods for calculating gas velocity, particle velocity, and particle stagnation time and rising height in gas-solid flow, have been developed through theoretical analysis, resulting in an eight-parameter expression, Eq. (14), for computing TDH. This equation, which contains more parameters than those in any previous work, gives closer fit to experimental results, and is thus recommended for design.