Periodical attenuation of particles, which interferes seriously the normal alumina production, exists in Bayer process. In order to solve this problem, the rule of periodical attenuation of Al(OH) 3 particles was investigated by laboratory experiments under simulated industrial conditions. The results show that at higher temperature the variation period of particle size is shortened, while prolongs with more solid content. Particle size fluctuation amplitude reduces with the temperature rising but increases with the solid content increasing. Particle size distribution becomes more uniform by replenishing fine seeds, enabling the periodical fluctuation of Al(OH)3 particle size to be attenuated. Combining properly the additives with controlling the seed size is able to reduce the amplitude of periodical fluctuation and shorten the attenuation time. With unbalance of particle size distribution, the particles gradually become bigger, even inducing the decrease of the specific surface area of seeds, which is the major reason causing explosive attenuation of Al(OH)3 particles in seed precipitation process.