Abstract: Separation mechanism of liquid-solid fluidized bed separator (LSFBS) was studied by using theoretical analysis and experimental researches.Characteristics of autogenous medium fluidized bed in LSFBS were analyzed and the influence of autogenous medium size on the separation performance of ISFBS was studied , taking quartz particles of various sizes as autogenous medium.According to the separation results ,a better segregation could be achieved by using finer autogenous medium.Particularly , the optimum of Evalue of 0.15~0.2 mm quartz was 0.053 while that of 0.25~0.45 mm quartz increased to 0.095.Finally , the influence of size distribution of feed and operating conditions on the separation efficiency was analyzed.Reducing feed size range and enlarging lower-size limit of feed could improve the device performance.Under a certain bed pressure ,a smaller upward current velocity could generate a higher solid volume fraction and bed effective density.A smaller upward curent velocity could also decrease the influence of size and shape on the movement of particles.All of these changes could induce a better separation performance for LSFBS.