The excitation properties of the surface plasmons (SPs) excited by the metallic parallel-nanorod and U-shaped nanostructures are simulated under the illumination field conditions of pulse plane wave and circular high numerical aperture focal evanescent field using the finite difference time domain (FDTD) method. Under the illumination of pulse plane wave, the two nanostructures present the same surface plasmon resonance (SPR) wavelength in the visible range. After that, we simulate the excitation properties of SPs excited by the two nanostructures in the fields of the circular high numerical aperture focal evanescent beam with the same SPR wavelength. The simulation results indicate that the U-shaped nanostructure performs the best local field enhancement and far field transmission ability, which can be used to construct a plasmonic tweezer for trapping nano-particles.