The tracking capability of tracer particles is one of the key points to the applications of PIV technique in supersonic flow.In this paper,the experiment research of PIV technique was developed in Multi-Mach number High-speed Wind Tunnel of SJTU,and an analytical model of relaxation characteristics was specially proposed,which used to evaluate the tracking capability of tracer particles.In the supersonic flow of Ma4,the results of the PIV experiments on typical models,including a sharp cone and two wedges with different semiapex angles,agree well with the analytical results of the particle diameters,and demonstrate the measurement accuracy and the seeding efficiency of PIV in the supersonic flow.It indicates that the proposed model is prac-tically credible to analyze the relaxation characteristics of tracer particles.