In Circular Synthetic Aperture Radar(CSAR), the range equation between radar and ground moving target is complicated because the radar platform flies around the circumference of the observation scene, and there is a complex coupling relationship between range direction parameters and azimuth direction parameters of target , which makes it difficult to estimate the range velocity of moving target independently. A method for estimating the range velocity of moving target in terahertz CSAR based on sub-aperture division is proposed. By selecting a suitable angle of sub-apertures , sub-aperture division is performed on CSAR. Under the condition of sub-aperture, the decoupling between the range velocity of moving target and other parameters can be realized by small angle approximation , and the range velocity of moving target can be accurately estimated , which can achieve accurate relocation of moving target . The effectiveness of the proposed algorithm is verified by simulation and measured data.