The method and device for filtering liquid in an aquarium, the filtration device made by the liquid filtration method comprises a box-shaped casing (1), the filtration bodies and filtration materials are set inside the casing, wherein the casing (1) includes a water inlet (13) set around the casing (1) and grid panels set inside both sides of the casing (1)； the filtration bodies include an inner filtration body set inside the grid panels and an outer filtration body set outside the grid panels； the filtration materials are filled inside the casing (1), between the inner filtration body and grid panels； in this way, the liquid to be filtered enters into the casing (1) through the water inlet (13) and flows out from the grid panels, and proceeds further from the casing (1) via the inner filtration body, filtration materials and outer filtration body treatment. The liquid filtration device has the advantages of being an integrated replacement as a filtration consumable, good universality, convenient installation and maintenance, large filtration area and effective prevention of dirt left after filtration from a backflow.
