Plasmonic nanoperiodic Ag nanoparticle arrays with hexagonal close-packed structures and different symmetries were synthesized by localized surface plasmon resonance (LSPR) induced chemical growth. When the plasmonic nanostructure was excited by a laser, the neighboring silver nanoparticles generated high local electric field enhancement for surface-enhanced Raman spectroscopy (SERS), which was used to show the relationship between the axisymmetry of the plasmonic nanostructure and the SERS polarization effect. The experimental results indicate that the optimal axisymmetric structure (six-axis symmetric) exhibited the strongest SERS polarization-dependence, whereas the disordered structure with an arbitrary axis exhibited a relatively weak SERS polarization dependence. To clarify the root cause of SERS polarization dependence, the electric field enhancement distribution for the plasmonic nanostructures was numerically simulated based on S-and P-polarization excitation. Most importantly, the fundamental reasons for the polarization dependence of SERS were obtained by the quantitative numerical simulation of the hotspot distribution for the plasmonic nanostructures.