Abstract: In the process of preparation of titanium dioxide by the sulphuric acid method，fine filtration is necessary for the treatment of black liquor produced by the primary deposition after acidolysis of ilmenite.Wood powder is employed as a conventional filter-aid for fine filtration，but it encounters ecological and environmental pressure due to the great need of lignum for its production.In this work，a new type of filter-aid of diatomite was developed.The optimum parameters (such as the amount of diatomite，the pre-heating temperature of black liquor and the stirring time) of fine filtration process with the diatomite filter-aid were decided by orthogonal experiment.It was demonstrated by related industrial experiments that the filtrated amount of black liquor was increased by 80.6% after the displacement of wood powders by diatomite in same conditions，while its cost was only 64.5% of wood powders.