The ability to control the local surface plasmonic resonance (LSPR) absorption peaks of silver nanoparticles will greatly broaden the scope of their practical application. Conventional methods tune the LSPR peaks by modifying the shape or size of the silver nanoparticles. Here, we present a novel method to tune the LSPR band by controlling the particle corner sharpness. A modified photochemical method was used to prepare silver nanoparticles. It was found that the nanoparticles irradiated using light-emitting diodes (LEDs) with a wavelength of 455 nm were decahedral, although the reaction temperature was different. However, the in-plane dipole LSPR peak of the as-prepared silver nanodecahedra exhibited an evident red shift from 460 nm to 500 nm during the synthesis process, and the wavelength of the LSPR peak increased linearly as the reaction time increased. A numerical simulation conducted to investigate the mechanism behind the shift revealed that the red shift of the LSPR peak was mainly induced by the evolution of the corner sharpness of the silver nanodecahedra. These results demonstrated the effectiveness of the method in precisely tuning the LSPR peak by controlling the reaction time. By turning off the irradiation light, the photochemical process could be immediately terminated, and the LSPR peak of the silver nanoparticles remained constant. Compared with conventional methods, the present tuning precision can reach 1 nm.