The traditional nano preparation method is costly and time-consuming, and contains hazardous chemical constituents, thus affecting the characteristics and applications of nanocolloid. The Electrical Spark Discharge Method (ESDM) used in this paper prepares Nano-Ag colloid in deionized water, which is characterized by low cost, continuous and rapid production, and is free of chemical substances. According to the UV-Vis analysis of Nano-Ag, it has a peak at about 392 nm. Based on Zetasizer analysis, the minimum size is distributed below 50 nm, and the zeta potential is about −35 mV which the value of pH is almost equal to 7, proving its good suspension stability. According to the results of SEM, Nano-Ag colloid prepared by ESDM has nanoscale particles, and the constituent is Ag only. As this method is free of any surfactants and chemical agent, the Nano-Ag is added in the human body by imitating agar, and coated with Niger, the Nano-Ag restrains the growth of Niger. The higher the concentration of Nano-Ag, the stronger the inhibitory effect on the growth of Niger.