Abstract: Particles’ simplified motion equations were solved using the fourth order Runge-Kutta algorithm and their settling velocities as well as displacements along with time in liquid-solid fluidized bed separator were obtained. Fluid-ization experiment system was set up to verify the correctness of the calculated values of hindered settling velocities from solving particles’ simplified motion equations. The relative error of calculated hindered terminal settling veloci-ties could be kept within 5% overall compared with the experimental values. Then,a mathematical model for liquid-solid fluidized bed separator was proposed based on particles’ simplified motion equations. The predicted partition values of different density fractions were validated with separation experiment, demonstrating that the mathematical model used in this work could give a well enough predicted separation result with a root-mean-square error of 5. 05 of all density fractions. Using the mathematical model,the influence of feed rate on the separation results was explored, indicating the decreasing of the ratio of fluidized bed effective density ρeff to δ50 ( separation density) was the reason that separation efficiency decreased with the feed rate increasing.