The invention discloses a filtering device and a filtering method for reducing nuclear power filtering solid waste quantity. The filtering device comprises a filter shell, a filter element assembly, a water inlet pipe, a water outlet pipe, a water inlet valve, a water outlet valve and a filter element cleaning structure, wherein the filter element assembly is arranged inside the filter shell, a water inlet and a water outlet are formed in the filter shell, a water inlet pipe is arranged at the water inlet, and a water inlet valve is arranged on the water inlet pipe; the water outlet pipe is arranged at the water outlet and is provided with a water outlet valve; and the water inlet is positioned below the water outlet. According to the filtering device, the filter element cleaning structure is arranged, the filter element assembly can be cleaned and regenerated, the problem that an original filter element cannot be recycled is solved, the filtering device is adopted for filtering, long-term operation can be achieved, the filter element does not need to be frequently replaced, and the filtering device has the advantages of reducing the maintenance frequency, reducing the solid waste output of the filter element and reducing filter element solid waste quantity. And the device is suitable for radioactive water filtration of the nuclear power station.