This article discusses the effects of reducing agents on metallic nanoparticles, especially dumbbell-shaped metal nanoparticles. In this experiment we discuss the synthesis of Au nanorods (AuNRs) and Au nanodumbbells (AuDBs) as core to format Au-Ag core-shell nanoparticles. In this experiment, the cationic interface surfactant was used as a protective agent to synthesize the AuNRs, and the AuNRs were modified into the AuDBs under the same environment. By using the synthesized AuNRs and AuDBs reduce silver ions in the condition of normal temperature and high temperature to form a silver shell on the surface of the AuNRs. The order of addition of the reducing agent affects the shape of the coated silver shell, which has a rectangular parallelepiped, a double triangular pyramid, and an irregular shape. These three kinds of silver shell each occupy a certain proportion. The effect of the reducing agent used in the silver coating on the surface of the Au nanoparticles was studied after the modification of the Au nanoparticles. Experimental results show that the reducing reagent could decrease the uncontrollable irregular shape ratio, increasing the proportion of the double triangular cone, and the mechanism of the control of gold core silver shell type and uniformity was further proposed.