The utility model discloses a bi-cyclic bio-film anammox reactor. A unique cyclone water distributor is arranged on the lower portion of the reactor. Flexible packing, a screen, floating balls, a three-phase separator and a downcomer are disposed inside the reactor. A return water outlet pipe, a return water inlet pipe and an overflow weir are disposed on the outer side of the reactor. The bi-cyclic bio-film anammox reactor has the advantages that 1, the cyclone water distributor can generate tangential flow so as to guarantee uniform water distribution and to favor intensification of mass transfer, 2, the flexible packing disposed inside the reactor can detain sludge, intensify treatment effect and shorten start time, 3, the screen and the floating balls can eliminate gas steaming, relieve disturbance of ascending bubbles to a precipitation zone, 4, return flow of the downcomer can intensify mixture in a reaction zone, improve mass transfer effect, dilute inlet water and increase impact load resistance of the reactor, return flows of the return water inlet pipe and the return water outlet pipe can maintain normal running of the reactor in initiate stage and low-load stage, and the inner return flow and the outer return flow can guarantee the reactor to highly efficiently and stably run under low load and high load.