In order to reveal the scattering characteristics of targets at terahertz frequencies, high resolution radar imaging was studied based on the high frequency (HF) electromagnetic calculation data. Considering huge data flow of 3D image formation, a novel azimuth-elevation imaging theory with its result similar to a photograph of targets was proposed. The point spread function is derived for revealing the high resolution performance and scatterers identification capability. Simulation results demonstrated that HF method can solve radar cross section of perfectly electrical conducting (PEC) target accurately and fast at terahertz frequencies. The high resolution images show that the sub-wavelength features of targets are resolvable. It also implies that terahertz radar can attain more fine information about targets, which will be helpful for target recognition.