Scanning electrochemical microscopy (SECM) is used to deposit gold nanoparticles on a glassy carbon electrode (GCE). Deposition conditions, including the tip-substrate distance, current density, substrate potential, and addition of Ag ions in the electrolyte are changed to study the effects on gold spot size and particle morphology. Atomic force microscopy (AFM) is used to analyze the gold nanoparticles. The size and shape of the nanoparticle can be controlled by different SECM experimental conditions. OMSOL Multiphysics software is used to simulate the results of SECM deposition. By comparing the simulation results and experimental results, the deposition process can be understood better. Heterogeneous irreversible reaction rate constant of the reaction happened on GCE can be estimated.