Silver nanoparticles have been synthesized by the reduction of AgNO3 in the presence of polyvinyl pyrrolidone as surfactant and ethylene glycol as reducing agent through a hot-injection method. The size distribution, morphology, structure and optical properties of particles have been characterized by transmission electron microscopy (TEM), X-ray diffractometer (XRD) and UV/Visible absorption spectrophotometry. While the absorption spectra was investigated by means of Mie theory. Results indicate that comparing to the traditional one-step reduction routes, the silver nanoparticles, derived from hot-injection method, possesses a better dispersion and more uniform size distribution. TEM images show that the morphology of nano-silver particles are spheroidal, with an average diameter of 20 nm, and the experimental observations are basically consistent with the numerical analysis results.