The extinction spectrum and sensor properties of the single hexagram Ag nanostructure were investigated. The calculation results by finite-difference time-domain method show that the peak wavelength of the extinction spectrum of hexagram Ag nanostructure has remarkable blueshift and the intensity is gradually weakened when the vertex angle increases from 20° to 140°. Vertex angle has great influence on the refractive index sensitivity, but little effect on the FWHM of the extinction spectrum. The refractive index sensitivity but not FWHM leads to the greatest figure of merit value for LSPR applications when vertex angle is 30°. For the situation with truncated vertices in experiment, analysis of the paper shows that truncation has an effect on extinction characteristics. In addition, the figure of merit gradually decreases with the degree of angle truncation increasing.