Abstract: The tracer's tracking ability is the key factor affecting the measurement accuracy of high speed PIV. Particle relaxation modeling is presented for high speed flow with the normal mach number over 1.4. Based on the combination of theoretical analysis and numerical simulations, high speed PIV and the tracer particle seeding technology are developed, and the quantificational measurement ability of PIV is improved. Recent experimental results were obtained by the Multi-Mach number high-speed wind tunnel in Shanghai JiaoTong university where titanium dioxides of various sizes were used as tracers in the Mach 4 wind tunnel to induce a 22° shock wave. The results reveal that the 30nm titanium dioxide particle is the most qualified option. Meanwhile, various shock wave experiments (including oblique shock wave and detached shock wave) were carried out to validate the particle tracing ability. In this paper, multiple experimental results are put forward to support the selection of tracer particles of high speed PIV.