Here we report a study on the role of chemical diffusion and reaction on the morphology evolution of silver particles. Electrochemical reaction is employed to synthesize silver particles. The reaction rate is regulated by current density while the diffusion rate of silver ions is regulated by the viscosity of solution. Silver dendritic particles are largely synthesized at various diffusion and reaction conditions. At a high reaction rate, silver dendrites are formed at the medium diffusion rates of silver ions while the dendritic structures are only formed at an extremely low diffusion rate of silver ions when the reaction proceeds slowly. Therefore, the interplay of diffusion and reaction plays a key role on the structure development of dendrites because the interplay determines the chemical distribution on the growth front of crystals. Once a chemical concentration gradient is established at the growth front, the dendritic structures is triggered.