Silver nanoplates were prepared in the solution of sodium dodecyl benzene sulfonate (SDBS) and polyvinyl pyrrolidone (PVP) via reducing silver nitrate with hydrazine hydrate. X-ray diffraction (XRD) and Scanning electron microscope (SEM) were applied to identify phase and observe microstructure. The surface tension analysis showed that in SDBS + PVP system, the γ-C curve acted as dual-platform and the corresponding concentration turning points were C1 (0.8g/L) and C2 (6.0g/L) respectively. XRD analysis confirmed that the reduction product was element silver. SEM observation revealed that nano-plates silver were obtained when the SDBS concentration was between C1 and C2, otherwise spherical-shaped nanoparticles were synthesized.