The invention discloses a water purifier filtering system which comprises a front filter element assembly, an RO membrane filter element and an activated carbon filter element which are sequentially connected in series together by virtue of water pipes. The invention also discloses a filtering method. The front filter element assembly is designed into a parallel combination of a first filter assembly, a second filter assembly and a third filter assembly, the first filter assembly comprises three composite filter elements connected in parallel with one another; the second filter assembly comprises a PP filter element and two composite filter elements connected in parallel with each other; the PP filter element is mutually connected in series with the two composite filter elements connected in parallel with each other; the third filter assembly comprises two PP filter elements connected in parallel with each other and a composite filter element; and due to the mode of mutually connecting the two PP filter elements connected in parallel with each other and the composite filter element, the problem that the filter element is blocked is solved, the filtering effect is good, the filter element needs to be replaced after being used by one year, and the maintenance cost is greatly reduced.