The utility model discloses a circulating clarifier for sludge, and the circulating clarifier comprises a mixing area, a flocculating area and a settling area; and the circulating clarifier for sludge is characterized by further comprising a sludge conditioning area, wherein the sludge conditioning area and the mixing area are both connected in series with the flocculating area, and the flocculating area is connected in series with the settling area. According to the utility model, through setting the independent sludge conditioning area, returned sludge before being fed into the flocculating area is conditioned, therefore, the density, spherical degree and uniformity of sludge as a flocculated core are improved, the flocculation effect is strengthened, and finally, high-density, high-spherical-degree and high-uniformity floccules can be formed, so that the operation effect of the clarifier is more stable, the hydraulic loading of discharged water of the clarifier is improved, the concentration of discharged sludge is enhanced, and the occupied area is reduced, therefore, the circulating clarifier for sludge can be applied to industrial feed-water treatment and wastewater treatment, and also can be used for carrying out treatment on municipal feed-water and drained water.