The large bandwidth signal of terahertz radar can achieve high resolution, meanwhile, it has higher requirements on the sampling rate and data processing capability of the system. A Complex Approximate Message Passing algorithm based on sparse recovery theory was proposed in this paper, which realized the reconstruction of echo signals at low sampling rate. The turntable model was used firstly to achieve two-dimensional imaging of the target. Then the Double Integration algorithm, the Complex Approximate Message Passing algorithm and the Fast Iteration Soft Threshold algorithm was used to reconstruct the target image. Comparison of the imaging results of the three algorithms verifies the superiority of the proposed algorithm.