The decline reasons of hydraulic filter filtration ratio in using process were analyzed by studying different hydraulic filter media and used filter. The results show that: the filter material processing in later stage will damage the structure of the filter media; in the working process，the increasing pressure difference between the inflow face and outflow face may also affect the structural stability of the filter media；nonwoven composite can make filter media maintain higher filtration ratio；when gluing on the filter media，ideal resin not only should be adapt to the hydraulic system but also can make better combination between the fibers，to ensure that the filter media maintains higher filtration ratio during the work.