Based on the electromagnetic loading device CQ-4, an experimental method of simultaneously measuring the refractive index and high pressure sound velocity of transparent material is established. The ramp wave compression experiment of PMMA is carried out under a pressure of 14 GPa. The velocity history curves of PMMA sample rear surface are obtained by dual laser heterodyne velocimetry (DLHV). The velocity curve shows obvious double wave structure, which indicates the elastic-plastic transition. The refractive index particle velocity optical characteristics and Lagrangian sound velocity particle velocity dynamic characteristics of PMMA are obtained simultaneously with the experimental data processing.