Silver nanoparticles colloid has been prepared by heat-combined electrochemical method, which uses simple and low-cost equipment of easy installation and operation, is easily deployed in industrial scale. A silver plate was used as the cathode instead of silver salts to avoid unexpected ions from the salts. The cathode was made from a stainless steel plate. The chemical used as the electrolyte solution is TriSodium Citrate. Silver nanoparticles made by the above method are spherical, small-sized, its size distribution ranges from 3-12nm, stably dispersing in a non-toxic solution. Bactericidal capacity of silver nanoparticles are tested on 4 types of common bacteria and fungi. The results showed that silver nanoparticles with a concentration of 10 ppm have a good bactericidal capacity against the said bacteria.