There is increasing interest in high-resolution radar imaging of targets, and the recent development of terahertz (THz) imaging technique provides the depiction ability of targets in detail. The compressed sensing theory is introduced into terahertz radar azimuth-elevation imaging for facilitating the increasing sampling pressure and obtaining the improved imagery by exploiting the block sparse structure of a target’s reflectivity distribution. Compared with the conventional processing of even block partition in block sparsity, a block-coherence definition for uneven block partition is proposed as a sensing configuration quality parameter, and its relationship to the imagery reconstruction performance is verified. Further, a contrast metric for evaluating the improved image of uneven block partition is discussed without the knowledge of a true imaging result. The electromagnetic calculation data are used for the verification of imaging.