The ice nucleating properties including nucleation rate, freezing temperature, freezing rate of nano-silver iodide (AgI) by using “37” shells in 20-L and 1200-L cloud chamber was studied. The results were compared with those obtained on the conventional silver iodide under the same experimental conditions. The results show that the ice nucleating properties of the nano-silver iodide are significantly better than those of the conventional silver iodide, its nucleation rate is increased by 2-3 orders of magnitude, freezing temperature rises, and freezing rate is significantly increased.