The invention discloses a fish tank filter device, and relates to the technical field of water filtering in fish tanks. The fish tank filter device comprises a distributive ring in the middle, an A filter assembly on the upper portion and a B filter assembly on the lower portion; a plurality of water outlet channels are evenly formed in the distributive ring in the circumferential direction; the outlets of the water outlet channels are arranged downwards in an inclined mode; electromagnetic flow valves are cooperatively installed in the water outlet channels respectively; distance sensors are fixed to the outlets of the water outlet channels on the outer wall of the distributive ring; the signal output ends of the distance sensors are connected with a microprocessor; the microprocessor is connected with the electromagnetic flow valves. The fish tank filter device has the advantages that the device can freely move in the water of a fish tank, the filter effect is good, and the efficiency is high; moreover, the use efficiency of filter cotton is improved, and the filter cotton is convenient to clean and change.