Coherence measurement system based on Self-Mixing(SM) interferometry with a Terahertz Quantum Cascade Laser(THz-QCL) has been demonstrated to be a highly sensitive sensor. Compared with traditional laser Doppler velocimetry, it has the advantages of self-collimation and eliminating the need for a separate photodetector and mixer, which makes the system more compact; moreover, the exploitation of terahertz source is expected to improve the upper limit of velocity measurement. In this paper, the nonlinear dynamic response to the motion of two independent targets is investigated, which manifests itself in the SM interferometric signal. Through the spectrum analysis of the SM signal, velocities and directions of the two targets are obtained. The research results demonstrate the feasibility of using THz-QCL SM interferometric system to sense the motion of targets, and provide a novel technique for laser Doppler velocity measurement of multiple targets with high speed.