To reduce the hardness in the water, the new-style granulation reactor with gravel packing is utilized. The reactor operates at 20°C. During the experiment, the content of absorbed calcium carbonate crystal in the gravel packing is measured by changing pH value, the diameter of the gravel packing, hydraulic condition and reacting time to investigate the performance of the reactor. Experimental result demonstrates that when the pH value is over 12, the diameter of the gravel packing was 0.2~0.5 mm; the feed water flow of raw water was 10~35 mL/s; the reactor has the optimal treatment efficiency. With the progress of the granulation reactor,it is found that the calcium carbonate crystal absorbed in the surface of the gravel padding gradually accumulates. When the reactor operates for about 15 days, the content of absorbed calcium carbonate crystal reaches saturated state, and the old packing could be replaced with new one. The reactor removed 58%~67% of the hardness in raw water.and the water quality of the effluent is good.