High resolution imaging is one of the main functions of Synthetic Aperture Radar(SAR). In order to validate a multiband terahertz radar imaging system which is going to be set up，this paper takes the Range Migration Algorithm(RMA) as an example，and presents a 2-D imaging simulation of a terahertz radar system with the carrier frequency of 675 GHz and the bandwidth of 20 GHz by Matlab/Simulink. Then the modules of echo generation，Range Compression，and Fast Fourier Transform(FFT) are designed based on Simulink and the high resolution 2-D images are obtained. The simulation results are consistent with the assumed targets and scenes，which verifies the validity of the simulation system. In the end，the improvement and analysis on the problems occurring in the simulation results are performed.