A filter tank convenient for replacing the filter materials is provided, which is characterized in that the upper end and the lower end of the tank are separately equipped with a filter material inlet and a filter material outlet, and the filter material inlet and outlet are sealed by the flanges and the flange covers. The utility model has the advantages that the replacement of the filter materials is convenient. When replacing the filter materials, the two flange covers shall be opened, and the old filter materials will be discharged from the filter material outlet of the lower end. After sealing the filter material outlet, the new filter material shall be added from the filter material inlet of the upper end. After sealing the filter material inlet, the filter tank can be normally used.