The uniformly dispersed silver nanopowders were prepared by even precipitation combined with thermal decomposition. The formation mechanism of silver nanopowder was investigated. The effects of pH value, calcination temperature and time on the size and morphology of the silver nanopowder were studied. The structure, composition, size and morphology of silver nanopowder were characterized by X-ray diffraction and scanning electron microscope. Results show that when the pH value is 7, calcinations temperature is 300 ℃ and the time 2 h, the obtained silver powders with an average size of 50 nm have excellent dispersion and uniform size. The method used for silver nanopowder production in this study has many advantages: the raw materials are easy to get and cheaper, the side-products in the production is recoverable with water, and the recovery can be used as a fertilizer in agriculture. Therefore, the processes can meet the requirements of clean-production of silver nanopowders.