Abstract: A flush valve diaphragm filter has a filter body forming a recess section for being assembled to a diaphragm. The filter body defines a main passageway longitudinally therethrough and a plurality of branch passageways transversely therethrough. The branch passageways communicate with the main passageway, and have diameters smaller than the diameter of the main passageway. The flush valve diaphragm filter effectively debases the ratio of fluid passage being fully clogged, and guides strip-like fibre and lichens to exterior. Correspondingly water filtering function is enhanced.