Based on the temperature-dependent complex dielectric constant of indium antimonide, an InSb-dielectric-InSb plasmonic waveguide structure with the grating was realized. At the frequency of 1 THz, a directional beam was obtained, and its radiation direction can be controlled by changing the temperature difference between the grating structures on each side. Finite difference time domain (FDTD) method was adopted to evaluate the relationship between the off-axis angle of the beam and the temperature difference. The tunable directional beaming can be attributed to the grating coupling of the TM surface modes in plasmonic waveguides.