A key factor in high-resolution synthetic aperture radar imaging is that the radar operates under ideal conditions. However, the motion trajectory of radar is usually not an ideal straight line or stable, so any small motion error within the synthetic aperture time can cause image blur or distortion. For small-scale imaging scenes, due to the susceptibility of GPS to signal interference and multipath effects, the traditional motion compensation method that combines GPS and INS data is not very effective. In this scenario, this study proposes a terahertz SAR imaging motion compensation method that only utilizes inertial navigation information. This method fully utilizes the velocity information provided by the inertial navigation system, establishes a radar motion trajectory model, and effectively estimates the echo phase error in the radar line of sight direction, thereby achieving focusing on terahertz SAR imaging targets. The experiment used a SAR system with a center frequency of 0.2 THz for motion compensation, and analyzed the strong scattering points of SAR images before and after compensation. Compared with the existing technology based on GPS and INS joint motion compensation methods, the motion compensation method proposed in this study respectively improved by 0.7 and 0.8 dB on PSLR and ISLR. In terms of imaging speed, the motion compensation method proposed in this study also improved by 0.2%. The experimental results showed that the focusing effect of this method was better for small-scale imaging scenes, further verifying the correctness and effectiveness of the motion compensation algorithm mentioned in this study.