Periodical attenuation of particles, which interferes seriously with the normal alumina production, exists in Bayer process.In order to solve the problem, the rule of periodical attenuation of Al(OH)3 particles has been invetigeated under industrial conditions modeled in laboratory.The results show that the variation periods of particle size shortens with higher temperature and lengthens with more solid content, and that the fluctuation amplitude of the particle size reduces with rising of temperature and enhances with increasing of solid content.