The invention discloses an unpowered internal circulation biochemical reaction settling tower and a workflow thereof. The unpowered internal circulation biochemical reaction settling tower includes ananoxic reaction zone, an aerobic reaction zone, a settling zone, an internal circulation system, a water intake pump and an aeration fan. The bottom of the anoxic reaction zone is provided with a perforated water distribution pipe, the aerobic reaction zone is internally equipped with aeration devices and suspended filler from the bottom up, the settling zone includes sludge hoppers, inclined plate areas, a clear water area and effluent weirs, the internal circulation system includes a gas-liquid separation tank, a raising pipe, a reflux pipe and a gas collecting hood, and the anoxic reactionzone, the aerobic reaction zone and the settling zone are arranged from the bottom up, the water intake pump is communicated with the perforated water distribution pipe, the aeration fan is communicated with the aeration devices, the slope sides of the gas collecting hood and the slope sides of the sludge hoppers are staggered to form water seams, the gas collecting hood is communicated with thegas-liquid separation tank through the raising pipe, and the gas-liquid separation tank is communicated with the bottom of the anoxic reaction zone through the reflux pipe. The unpowered internal circulation biochemical reaction settling tower provided by the invention has the advantages of small floor area, low energy consumption, good removal effect of organic matters and total nitrogen, strongimpact resistance and the like.