The filtration ratio of hydraulic filtration material decreases seriously in the filtration process,which leads to shorten the service life of filtration material.In order to alleviate the phenomenon that the filtration ratio of the filter material decreases in the later stage of filtration,PET fibers with the same proportion and different diameters were added to the glass fiber filter material.By testing the tensile strength of the filter material,it was proved that the addition of 0.1 D ultrafine PET fiber is beneficial to improve the strength of the filter material.Finally,the multi-pass performance of the pure glass fiber filter media and the 0.1 D ultrafine PET fiber media containing 15% was tested.The results show that the tensile strength of the 0.1 D ultrafine PET fiber with the addition ratio of 15% is the highest.It is found through multi-pass test that at the same filtration accuracy,the filtration rate descent speed of the filter material added with 0.1 D ultrafine PET fiber is slower than that of pure glass fiber filter.