The surface plasmon polaritons of the topological insulator Bi2Se3 can be excited by using etched grating or grave structures to compensate the wave vector mismatch of the incident photon and plasmon. Here, we demonstrate novel gold grating/Bi2Se3 thin film/sapphire hybrid structures, which allow the excitation of surface plasmon polaritons propagating through nondestructive Bi2Se3 thin film with the help of gold diffractive gratings. Utilizing periodic Au surface structures, the momentum can be matched and the normal-incidence infrared refl ectance spectra exhibit pronounced dips. When the width of the gold grating W (with a periodicity 2W ) increases from 400 nm to 1500 nm, the resonant frequencies are tuned from about 7000 cm?1 to 2500 cm?1. In contrast to the expected√q dispersion for both massive and massless fermions, where q～π/W is the wave vector, we observe a sound-like linear dispersion even at room temperature. This surface plasmon polaritons with linear dispersion are attributed to the unique noninvasive fabrication method and high mobility of topological surface electrons. This novel structure provides a promising application of Dirac plasmonics.