In the production process of flame retardant fibers, a large number of white viscous impurities formed by reaction molding of flame retardant adhesiv through spinning machine and spinning bath in acid bath, can't be effectively remove using some conventional filter method, so scaling is formed in pipeline and equipment, resulting in a significant increase in production operation load and equipment maintenance costs. A small-scale experiment was carried using a new filtering method—Fenda filter. The experimental results show when 200 type filter cloth is used, the content of diatomite is 10 g/L , the filtration pressure control is 0.4 ~0.5 MPa, the time of regenerative cleaning is 30 minute, the Fenda filter can effectively remove all kinds of impurities produced in the process of combustion-supporting fiber production, the transparency of bath liquid is improved, and make the turbidity index from undetectable value to less than 50 FTU after filtration, thereby achieving the requirements of production targets.