Abstract: In order to give a reference for further improving the national standard GB 24265-2009，the baked diatomite filter aid(ZBS) and fluxing baked diatomite filter aid(BS) which were both produced for medicine and food in Linjiang diatomite filter aid factory were used as sample，and the testing device of diatomite filter aid's permeability was used to investigate the influence of particle size on the permeability of the ZBS and BS. The result showed that the equations of the permeability changing with the particle size of the two samples were in accord with the linear equation of direct proportion. But the particle size of ZBS sample had a more apparent effect on the permeability. When the particle size of the two samples was the same，the permeability of the ZBS was higher than the BS'. Through the linear regression equation of the relationship between permeability and granularity，it could be concluded that the d₅₀'s range of ZBS for medicine and food should be 24.6~131.4 μm，and the d₅₀'s range of BS for medicine and food should be 2.9~79.8 μm.

Key words: Diatomite filter aid in food and medicine, Particle size, Penetration rate